Microstructural Observations Research Articles

Influence of discrete laser surface melting on scuffing resistance of W6Mo5Cr4V2 steel gear

Abstract The gear transmission system is advancing towards high-speed and heavy-duty applications. Among the main failure modes of the system, tooth surface scuffing due to increased tooth surface temperature has emerged as a prominent concern in mechanical transmission. Addressing the enhancement of gear scuffing resistance has thus become an urgent challenge in this field. This paper utilized discrete laser surface melting (DLSM) treatment to create discrete laser surface melted (DLSMed) units on the surface of W6Mo5Cr4V2 steel gears, resembling the radial ribs found on the surface of Limaria basilica. The paper investigated the size, hardness, residual austenite content, and residual stress of the DLSMed units at varying current intensities and laser frequencies. Microstructural observations were conducted on the DLSMed units, followed by gear scuffing experiments performed on the Forschungsstelle für Zahnräder und Getriebebau (FZG) testing machine. The experimental findings revealed that the change in laser frequency had a clearly weaker impact on the size of the DLSMed unit compared to current intensity. The DLSMed unit consisted of two parts: the melting zone (MZ) and the heat-affected zone (HAZ), with equiaxed and dendritic microstructures, respectively. Both zones exhibited refinement with increasing current intensity and laser frequency. Moreover, the microhardness of the DLSMed unit showed significant improvement compared to that of as-received gears. The scuffing resistance of DLSMed gears was found to be closely linked to their initial surface roughness. Residual stress formation in DLSMed gears was attributed to thermal stress and microstructural stress. The distribution pattern of DLSMed units had varying effects on the scuffing load-carrying capacity of DLSMed gears. Specifically, DLSMed gears with transverse distribution of DLSMed units demonstrated a 12.5% improvement in anti-scuffing performance compared to those with longitudinal distribution. Finally, this paper elucidated the mechanism through which DLSM enhances the scuffing resistance of W6Mo5Cr4V2 steel gears.

Multi-material structures of Ti6Al4V and Ti6Al4V-B4C through directed energy deposition-based additive manufacturing

The demand for advanced materials has driven innovation in titanium alloy design, particularly in the aerospace, automotive, and biomedical sectors. Additive manufacturing (AM) enables the construction of multi-material structures, offering potential improvements in mechanical properties such as wear resistance and high-temperature capabilities, thus extending the service life of components such as Ti6Al4V. Directed energy deposition (DED)-based metal AM was used to manufacture radial multi-material structures with a Ti6Al4V (Ti64) core and a Ti6Al4V-5 wt.% B4C composite outer layer. X-ray diffraction analysis and microstructural observation suggest that distinct B4C particles are strongly attached to the Ti6Al4V matrix. The addition of B4C increased the average hardness from 313 HV for Ti6Al4V to 538 HV for the composites. The addition of 5 wt.% B4C in Ti6Al4V increased the average compressive yield strength (YS) to 1440 MPa from 972 MPa for the control Ti6Al4V, i.e., >48% increase without any significant change in the elastic modulus. The radial multi-material structures did not exhibit any changes in the compressive modulus compared to Ti6Al4V but displayed an increase in the average compressive YS to 1422 MPa, i.e., >45% higher compared to Ti6Al4V. Microstructural characterization revealed a smooth transition from the pure Ti6Al4V at the core to the Ti64-B4C composite outer layer. No interfacial failure was observed during compressive deformation, indicating a strong metallurgical bonding during multi-material radial composite processing. Our results demonstrated that a significant improvement in mechanical properties can be achieved in one AM build operation through designing innovative multi-material structures using DED-based AM.

Study of the effects on the Strengthening Mechanism and Wear Behavior of Wear-Resistant Steel of Temperature Controlling in Heat Treatment

To improve the wear resistance of the materials used for blades in engineering machinery, this study focused on the microstructural characteristics, mechanical properties, and wear behavior of HB500 grade wear-resistant steel developed using an optimized heat treatment system. To improve the temperature uniformity of the heat treatment furnace, the method of cyclic heating was used to heat the components. Carefully designing the quenching equipment, such as using a cross-shaped press, was employed to enhance the quenching effect and reduce the deformation of the steel plates. The crystal orientation analysis revealed a uniform and fine-grained microstructure, primarily characterized by plate-type tempered martensite, which indicated a good hardenability. The microstructure observations showed that the width of martensite is approximately 200 nm, with a significant presence of dislocations and carbides. Tensile tests and multi-temperature gradient impact tests indicated superior mechanical properties compared to similar grade wear-resistant steels, including a Rockwell hardness of 53, tensile strength of 1610 MPa, yield strength of 1404 MPa, and total elongation around 12.7%. The results of friction and wear experiments indicate that the wear rate decreases as the load increases from 100 N to 300 N, demonstrating an excellent wear resistance under a large load. Observations of the worn surfaces indicated that the wear mainly involved adhesive wear, fatigue wear, and oxidative wear. The properties’ improvements were attributed to microstructure refinement and precipitation strengthening. This study indicates that designing a heat treatment system to control temperature uniformity and stability is feasible.

Microstructural analysis of titanium alloys based on high-temperature phase reconstruction

AbstractThe microstructural evolution of titanium alloys under high-temperature conditions plays a key role in determining their mechanical properties and hot working behavior. This research presents an advanced method for calibrating β phase reconstruction software using in situ testing on Grade 2 titanium, which achieves accurate reconstruction of the parent β phase microstructure. In addition, unique microstructural observations in the forging of Ti-6246 titanium alloy are highlighted, demonstrating the influence of deformation parameters on the resulting β phase grain structures. Using advanced techniques such as electron backscatter diffraction and Burgers orientation relationship-based software, the research elucidates the behavior of these phases under varying thermal and deformation conditions. In Grade 2 titanium, significant grain growth and phase transformation dynamics were observed upon heating beyond the β-transus temperature during in situ calibration of β phase reconstruction software. The analysis demonstrates the effectiveness of the software in precise reconstructing the parent β phase microstructure based on the orientation of the inherited αs phase. Furthermore, the evaluation of hot forming parameters in Ti-6246 alloy shows the influence of deformation temperature and strain rate on the resulting microstructure. Finite element method analysis coupled with dynamic material modeling elucidates the distribution of temperature, strain rate, and effective strain during forging, which aids in the qualitative assessment of hot workability. Microstructural observations in Ti-6246 alloy forging highlight the presence of elongated colonies of αs phase precipitates, indicative of localized strain intensities and deformation temperatures. In addition, EBSD analysis coupled with β phase reconstruction reveals distinct microstructural features in different regions of the forging. In particular, regions subjected to higher strain rates exhibit elongated β phase grains with pronounced disorientation gradients, suggesting intense deformation. Conversely, optimal forging conditions lead to the appearance of unreinforced axisymmetric β phase grains, indicating dynamic recovery processes. Pole figure analysis further emphasizes the Burgers crystallographic relationship between the αs and β phases, confirming that deformation during forging occurs exclusively within the β phase. These results provide valuable insights into the microstructural evolution in titanium alloys under high-temperature conditions, which are essential for optimizing hot working processes and improving mechanical properties. Graphical abstract

Dynamic Response of Ti-6Al-2Zr-1Mo-1V Alloy Manufactured by Laser Powder-Bed Fusion

Titanium parts fabricated by additive manufacturing, i.e., laser or electron beam-powder bed fusion (L- or EB-PBF), usually exhibit columnar grain structures along the build direction, resulting in both microstructural and mechanical anisotropy. Post-heat treatments are usually used to reduce or eliminate such anisotropy. In this work, Ti-6Al-2Zr-1Mo-1V (TA15) alloy samples were fabricated by L-PBF to investigate the effect of post-heat treatment and load direction on the dynamic response of the samples. Post-heat treatments included single-step annealing at 800 °C (HT) and a hot isotropic press (HIP). The as-built and heat-treated samples were dynamically compressed using a split Hopkinson pressure bar at a strain rate of 3000 s−1 along the horizontal and vertical directions paralleled to the load direction. The microstructural observation revealed that the as-built TA15 sample exhibited columnar grains with fine martensite inside. The HT sample exhibited a fine lamellar structure, whereas the HIP sample exhibited a coarse lamellar structure. The dynamic compression results showed that post-heat treatment at 800 °C led to reduced flow stress but enhanced uniform plastic strain and damage absorption work. However, the HIP samples exhibited both higher stress, uniform plastic strain, and damage absorption work owing to the microstructure coarsening. Additionally, the load direction had a subtle influence on the flow stress, indicating the negligible anisotropy of flow stress in the samples. However, there was more significant anisotropy of the uniform plastic strain and damage absorption. The samples had a higher load-bearing capacity when dynamically compressed perpendicular to the build direction.

Evidence for suboceanic small-scale convection from a “garnet”-bearing lherzolite xenolith from Aitutaki Island, Cook Islands

Garnet peridotite xenoliths have been rarely reported from suboceanic mantle. Petrographic and geochemical characteristics of garnet-bearing oceanic peridotite xenoliths provide precious information on dynamics of the suboceanic lithosphere and asthenosphere interaction. We examined a lherzolite xenolith included in olivine nephelinite lava from Aitutaki Island, a member of the Cook-Austral volcanic chain. The lherzolite xenolith contains reddish fine-grained (< 5 µm in size) mineral aggregates (FMAs) with size range of 0.5–6 mm, consisting of olivine, calcic and sodic plagioclases, aluminous spinel, native iron, and nepheline. Microstructural observations and chemical data corroborate that the FMA is a decomposed pyrope-rich garnet including chromian spinel grains with an irregular highly indented morphology in the center. The FMA is surrounded by pyroxene-poor and olivine-rich aureole. The spatial and morphological relationships of FMA and chromian spinel with pyroxene-depleted margin suggest a reaction of aluminous spinel + pyroxenes → pyrope-rich garnet + olivine, which requires a compression before decomposition of the garnet to FMA. An orthopyroxene grain shows slight but clear chemical zoning characterized by increase in Al, Ca, and Cr from the grain center to the rim. The zoning patterns of Al and Ca in the orthopyroxene grain can be modeled by diffusion-controlled solid-state reactions induced by pressure and temperature changes, keeping surface concentrations in equilibrium with the other coexisting mineral phases. The results indicate that the mantle, from which the lherzolite xenolith was derived, underwent isothermal decompression followed by a weak heating on a time scale of a few tenths of million years before the xenolith extraction. From the deduced compression and decompression histories, we hypothesize that the mantle beneath Aitutaki Island was once dragged down to a garnet-stable deep mantle region and brought up later by small-scale sublithospheric convection.

Extension of a phase-field KKS model to predict the microstructure evolution in LPBF AlSi10Mg alloy submitted to non isothermal processes

The out-of-equilibrium heterogeneous microstructure typical of AlSi10Mg processed by Laser Powder Bed Fusion (LPBF) is often modified by further heat treatment to improve its ductility. According to literature, extensive experimental investigations are generally required in order to optimize these heat treatments. In the present work, a phase-field approach is developed based on an extended Kim–Kim–Suzuki (KKS) model to guide and accelerate the post-treatment optimization. Combined with CALculation of PHAse Diagrams (CALPHAD) data, this extended KKS model predicts microstructural changes under anisothermal conditions. To ensure a more physical approach, it takes into account the enhanced diffusion by quenched-in excess vacancies as well as the elastic energy due to matrix/precipitate lattice mismatch. As the developed model includes the computation of the evolution of the thermo-physical properties, its results are validated through comparison with experimental DSC curves measured during the non-isothermal loading of as-built LPBF AlSi10Mg. The computed microstructure evolution reproduces the microstructural observation and successfully explains the peaks in the DSC heat flow curve. It thus elucidates the detailed microstructural evolution inside the eutectic silicon phase by considering the growth and coalescence of silicon precipitates and the matrix desaturation.

Hot deformation behavior and processing workability of a powder forged Fe-2.1Cu-0.5C alloy

Abstract Hot deformation behavior of as-sintered Fe-2.1Cu-0.5C alloy was evaluated through the construction of constitutive equations and a hot processing map. The hot deformation behavior was investigated at different temperatures and strain rates and microstructure observations were subsequently conducted. Flow stress for the initiation of dynamic recrystallization mechanism was determined. Tensile and fatigue strength tests were investigated at room temperature. It was observed that the microstructure of the alloy forged at lower temperature exhibited smaller grain size and its grain size increased with higher forging temperatures. Mechanical testing results revealed that an increase in the forging temperature led to a lower tensile strength and a higher fatigue strength. This change can be attributed to the larger grain sizes and the reduction of microcracks. A forging temperature at 1050 ℃ was recommended to achieve optimal mechanical properties for powder forged Fe-2.1Cu-0.5C products. These results might give some hints for optimizing process conditions and improving mechanical properties of powder metallurgy alloys by the use of constitutive equations and thermal processing maps.&amp;#xD;

Microstructural Analysis and Microhardness Evaluation of Stainless Steel SS304 Joints Utilizing Microwave Hybrid Heating (MHH) and Cold/Heat Processing: A Fuzzy Logic Approach

Stainless steel SS304 is extensively used in dental applications for its high strength, hardness, and corrosion resistance. However, Conventional dental joining techniques such as soldering and fusion welding, reliant on elevated temperatures and toxic fluxes, present substantial oral health risks, leading to potential health deterioration due to toxic emissions. The study proposes the utilization of a microwave hybrid heating process (MHH) for joining stainless steel SS304 (15mm × 7.9mm × 0.2mm) and pure zinc metal powder (44 µm, 99% purity), citing its enhanced efficiency, speed, precision, and diminished environmental footprint as key characteristics without fume. It explores heat processing between 30°C to 60°C and cold temperature processing from 0°C to 10°C to analyze alterations in hardness properties and microstructures. The study identified a direct correlation between temperature and microhardness, observing an increase in microhardness with rising temperatures. Optimal microhardness of 208.6 HV was achieved at 60°C during a 3 min heat treatment. Cold temperatures induced slight deformation and grain transformation, while heat treatment enhanced grain density and hardness, particularly in the strongly bonded boundary layer, with experimental and predicted values using Fuzzy logic showing promising outcomes and errors below 10%. In conclusion, the study demonstrates that achieving a specific hardness value in stainless steel joints is highly desirable for dental applications, alongside the observation of favorable microstructures. These findings underscore the potential of MHH to propel dental technology forward and promote sustainable practices while addressing environmental concerns.

Cryogenic deformation behavior, constitutive modeling and microstructure evolution of solution-treated 2195 Al-Li alloy at high strain rates

In this paper, the flow behavior, constitutive model and microstructure evolution of solution-treated 2195 Al-Li alloy at temperatures from 123 K to 298 K and strain rates from 2000 s-1 to 5000 s-1 were studied. Experimental results show that the flow stress of the solution-treated 2195 Al-Li alloy is more sensitive to deformation temperature than strain rate. As the temperature declines from 298 K to 123 K, the flow stress at 2000 s-1 and 5000 s-1 increases by nearly 32.8% and 34.5%, respectively, whereas as the strain rate increases from 2000 s-1 to 5000 s-1, the flow stress at 298 K and 123 K only increases by 5.1% and 6.5%, respectively. The average strain hardening rate tends to decline with the increase in strain rate and temperature, and its value at 123 K and 2000 s-1 is about 2.5 times that at 298 K and 5000 s-1. To overcome the limited applicability of the conventional Arrhenius model with strain compensation, an Arrhenius-based model (c-Arrhenius mode) is developed by coupling an independent strain term and derived using normalized flow stress and linear regression. To quantify the strain rate effect and temperature effect, a Johnson-Cook-based model (c-Johnson-Cook model) with exponential equations is developed. These two new constitutive models are validated via a comparative analysis, showing good predictability and accuracy. A further microstructure observation shows that the dislocation density is the highest at a strain rate of 5000 s-1 and cryogenic temperature of 123 K, which is beneficial for subsequent aging strengthening.

Optimization of the coating process in the PEGylated chitosan-based doped cobalt ferrite nanoparticles for hyperthermia applications using the Taguchi method

In this study, the parameters of coating process in the PEGylated chitosan-based doped cobalt ferrite nanoparticles for hyperthermia applications was optimized using the Taguchi method. The effect of chitosan and polyethylene glycol as well as the glutaraldehyde (crosslinker) contents on the structural, microstructural, and magnetic properties and the colloidal stability of the nanoparticles were investigated. Ultimately, to optimize the properties of the nanoparticles, the Taguchi method (L16 orthogonal array) was employed. The incorporation of the Ca2+ and Gd3+ into the spinel structure with an average crystallite size of 21 nm was successfully verified by X-ray diffraction (XRD) and the Rietveld refinement analysis. Moreover, thermogravimetric (TGA) analysis and Fourier-transform infrared spectroscopy (FT-IR) demonstrated the effective functionalization of the chitosan and polyethylene glycol coatings. Vibrating sample magnetometer (VSM) measurements revealed that saturation magnetization (Ms) was achieved in the range of 54.91–60.42 emu/g. Also, microstructural observations indicated that the coating layer can affect the particle size distribution and morphology. The Taguchi method identified that the glutaraldehyde content is the most expressive parameter influencing the nanoparticles’ properties, with the optimum properties achieved at chitosan, polyethylene glycol, and glutaraldehyde of 0.4 g, 0.08 g, and 1.2 ml, respectively. The antibacterial analysis confirmed the promising potential of the coated nanoparticles for biomedical applications. Furthermore, the magnetic heating efficiency of the synthesized nanoparticles was investigated in various concentrations of magnetic fluid, demonstrating their suitability for magnetic hyperthermia application.

Additive friction stir deposition of Al 6061-B4C composites: Process parameters, microstructure and property correlation

Al 6061-B4C metal matrix composites were fabricated using a novel solid state additive manufacturing technique of additive friction stir deposition (AFSD). Incorporation of B4C particles into the deposit was achieved by employing hollow Al 6061 feed stock filled with B4C powder and three different AFSD tool rotational speeds (200, 300 and 400 rpm). Fabricated deposits exhibited remarkable metallurgical bonding across the substrate/deposit interface and interlayer interfaces for all tool rotational speeds, indicating a wider fabrication window. A physics based pseudo-thermo mechanical model was employed to evaluate the thermo-kinetic conditions experienced by the depositing material to correlate with the microstructural observations. Deposited layers exhibited refinement of grains to ∼10 μm from the corresponding coarse grain structure of feedstock (136 μm). The regions near the B4C particles were observed to have finer grains (<2 μm) signifying particle stimulated nucleation. Although considerable loss in the tensile properties (60 % drop in yield strength) was observed in the AFSD deposits due to the associated dissolution of β’’ precipitates, subsequent heat treatment restored the tensile properties to the level of as received material (∼290 MPa). The thermo-kinetic conditions (temperature in excess of 500 °C and strain rates in excess of 250 s−1) experienced by the builds under higher AFSD tool rotational speeds (300 and 400 rpm) appeared to result in refinement of Al–Fe–Si based secondary intermetallic precipitates/dispersoids leading to the observed higher stability of their microstructure during the subsequent post AFSD heat treatment. Samples AFSD fabricated with a lower tool rotational speed of 200 rpm, however, exhibited significant grain growth on account of relatively larger secondary precipitates/dispersoids.

Thermoelectric Chalcostibite: Solid-State Synthesis and Thermal Properties

In this study, thermoelectric chalcostibite (CuSbS&lt;sub&gt;2&lt;/sub&gt;) compounds were fabricated using mechanical alloying (MA) and hot pressing (HP), and phase identification, microstructural observation, and thermal analysis were conducted. The thermal properties were then measured and compared with those of other Cu–Sb–S ternary compounds synthesized by the same solid-state process, namely, skinnerite (Cu&lt;sub&gt;3&lt;/sub&gt;SbS&lt;sub&gt;3&lt;/sub&gt;), famatinite (Cu&lt;sub&gt;3&lt;/sub&gt;SbS&lt;sub&gt;4&lt;/sub&gt;), and tetrahedrite (Cu&lt;sub&gt;12&lt;/sub&gt;Sb&lt;sub&gt;4&lt;/sub&gt;S&lt;sub&gt;13&lt;/sub&gt;). Both the MA powder and HP-sintered samples contained a single-phase chalcostibite with an orthorhombic structure, and relative densities of 94.6–99.7% were obtained based on HP temperature. The full width at half maximum of the X-ray diffraction peak was significantly reduced for the HP specimens compared to that of the MA powder due to stress relaxation and grain growth during HP at elevated temperatures. However, practically no changes were observed in the lattice constants based on HP temperature. Differential scanning calorimetric analysis revealed that one endothermic reaction occurred at 814–815 K for the MA powder and at 818–821 K for the HP specimen, which were interpreted as the melting points of chalcostibite. Densely sintered compacts with densities close to the theoretical density were obtained using HP at temperatures of 623 K or higher. The constituent elements of the chalcostibites were uniformly distributed. As the HP temperature increased, thermal diffusivity and conductivity increased, but they decreased significantly as the measurement temperature increased. For the chalcostibite specimen hot-pressed at 623 K, the thermal diffusivity and conductivity were (0.75–0.36) × 10&lt;sup&gt;-2&lt;/sup&gt; cm&lt;sup&gt;2&lt;/sup&gt; s&lt;sup&gt;-1&lt;/sup&gt; and 1.47–0.72 W m&lt;sup&gt;-1&lt;/sup&gt; K&lt;sup&gt;-1&lt;/sup&gt; at 323–623 K, respectively. Compared with other Cu–Sb–S ternary compounds, the thermal diffusivity was higher at low temperatures but similar at high temperatures, and the thermal conductivity above 500 K was lower than 1 W m&lt;sup&gt;-1&lt;/sup&gt; K&lt;sup&gt;-1&lt;/sup&gt;.

Conjugatal extrusion with dextral deformation in the Southeast Tibet: New insight into the Oligo-Miocene deformation in the Southeast Tibet

The Southeast Tibet has experienced significant deformation during the Late Cenozoic period, characterized by clockwise block rotation and separated by left-lateral strike-slip faults. Through our new field survey, structural analyses and microstructural observations, we have identified an early phase of ductile shear zones along three major faults: the Anninghe, Jinhe-Jinghe fault and Jinpingshan faults. New geochronological and thermochronological data collected from fault zones and carbonatites associated with a tear fault between two right-lateral oblique faults provides evidences that the slip occurred before ∼30 Ma. These new findings have led to a new conceptual model suggests that these NS-trending right-lateral oblique-slip faults, together with these NW-trending left-lateral strike-slip faults in Southeast Tibet, form a network of large conjugate fractures. The network was formed due to N-NE-trending contraction and played a crucial role in controlling the overall tectonic frame of Southeast Tibet during the Oligocene. By compiling and reviewing previous research with our latest findings, we propose that the region has undergone a transtion from oblique dextral to sinistral shearing since the Oligocene, providing new insights into the tectonic evolution of the East Tibet. Thematic collection: This article is part of the Mesozoic and Cenozoic tectonics, landscape and climate change collection available at: https://www.lyellcollection.org/topic/collections/mesozoic-and-cenozoic-tectonics-landscape-and-climate-change Supplementary material: https://doi.org/10.6084/m9.figshare.c.7262890

Microstructural Observations on the Durability of Stabilized Rammed Earth

This study provides a qualitative microstructural investigation of fly ash geopolymers' role in rammed earth's durability against water ingress and contact erosion. A series of SEM (scanning electron microscopy) images were captured on geopolymer-stabilized as well as unstabilized rammed earth samples. These samples were fabricated from predefined amounts of sand and fine materials together with fly ash geopolymers in the laboratory by static compaction to 25 MPa inside rigid molds. Two standardized durability tests were performed, namely, the dip test and the spray (also known as erosion) test. The results of these tests reflected excellent durability properties (practically zero erosion) of the stabilized material. The microscopic investigation provided an insight into the reason behind this improvement, where geopolymer networks inhabited the macro and micro pores and served as a cementing agent interconnecting the earthen materials’ grains. On the contrary, grains of the unstabilized material were weakly bonded by the clay component of the mixture, as observed with the SEM images; therefore, they were more susceptible to erosion by water.

Evaluation of the wear mechanism of ferromagnetic materials based on magnetic barkhausen noise

ABSTRACT As a typical form of damage, wear greatly affects the service properties of products, and non-destructive evaluation of the degree of wear is urgently needed. In this paper, the wear degree of AISI 1045 steel was evaluated by magnetic Barkhausen noise (MBN) testing. The root mean square (RMS) and full width at half maximum (FWHM) of MBN were extracted to establish the quantitative relationships between the tribological indicators and the stress state. The results indicate that the RMS decreases linearly and the FWHM increases quadratically with increasing tribological indicators, which can distinguish among different wear stages, including abrasive, adhesive and fatigue wear. However, the RMS shows a complicated nonlinear relation with the residual stress during the wear process. In addition, the MBN energy parameter is also calculated to reveal the features of the hysteresis loop at the wear scar. Both the coercivity H c and the maximum magnetic permeability μ max are linearly related to the tribological indicators and quadratically related to the stress, which reflects the effect of tribo-magnetisation on the MBN signals. The variation mechanism of MBN under different wear stages is attributed to the combined effect of plastic deformation and the stress state by microstructure observations.

Quasi-in-situ observation of fatigue crack growth behavior of friction stir welded 2024-T4 joint

This study presents a quasi-in situ observation of the fatigue crack growth behavior in a friction stir welded 2024-T4 joint. The microstructure and fatigue properties of the joint were investigated using electron backscatter diffraction (EBSD) technique, scanning electron microscopy (SEM), and fatigue crack growth tests. The fatigue crack growth behavior of the joint was examined by conducting fatigue crack growth tests with different notch locations. The results show that the sample with the notch in the stir zone (SZ) exhibited the highest resistance to fatigue crack growth, followed by the notched samples of the Advancing side (AS) and Retreating side (RS) weldments. Microstructural observations showed a homogeneous microstructure with a fine grain size in SZ and it was observed that this fine-grained structure significantly enhanced the material’s resistance to fatigue crack growth. The experimental results were further analyzed using the Paris model to provide a quantitative understanding of the crack growth behavior. The study underlines the impact of microstructural characteristics and notch location on the fatigue performance of the weldment. Overall, the quasi-in situ observations and experimental findings contribute to a comprehensive understanding of the fatigue crack growth behavior in friction stir welded 2024-T4 joints.

Self-similar nesting strategy enables lattices achieve dual energy-absorbing plateaus

Inspired by natural self-similar nesting (SN) strategy, the basic truss unit simple cubic (SC), face centered cubic (FCC), and body centered cubic (BCC) were regenerated into novel architected SN units, aiming to achieve dual-plateaus and improved energy-absorbing capacity compared to basic truss units. Through compression experiments, finite element analysis, microstructure observation and theoretical calculation, the SN lattices were investigated to explore the influence of the nesting ratio on the compressive responses. The optimal nesting ratio was verified as 0.4 for the unit size of 8 mm and the relative density of 20%, enable SN-SC and SN-FCC achieve the stable and excellent energy absorption capabilities. Furthermore, the underlying mechanism of dual-plateau achieved by SN strategy was revealed that a SN unit can be zoned into a stronger region containing the nested core SC/FCC and a weaker region consisting of exterior nest SC/FCC and mediation BCC. The higher yield strength of the nested core SC/FCC compared to the exterior nest SC/FCC and BCC actually cause the second higher stress plateau and the better failure-resistance for the SN lattices. The improvement effect of SN strategy on SC and FCC units indicates that SN strategy has the potential to be applicable to various strut-based units.

Kesan Tanpa Masa Pegangan Rawatan Haba ke Atas Sifat Mekanikal dan Mikrostruktur Pembuatan Aditif Aloi Titanum (Ti6Al4V) Melalui Proses Peleburan Laser Selektif (SLM)

Additive manufacturing (AM) or better known as 3D printing is a manufacturing method based on powder metallurgy technology that is able to produce a 3D component. Selective laser melting (SLM) is one of the AM methods capable of producing metal 3D components, however, residual stresses are often produced in such component due to repeated melting and solidification of metal during the printing process. The residual stresses can deteriorate the performance of the 3D components’ mechanical properties if not removed or reduced. Heat treatment processes are often used to remove the residual stresses. The basic parameters of heat treatment are heating temperature, heating rate, cooling rate and holding time. Based on the basic parameters, the effect of holding time in heat treatment is still less reported for 3D components printed via SLM. Therefore, in this study, the effect of holding time on the mechanical properties and microstructure of 3D titanium alloy (Ti6Al4V) components was intestigated. A total of 9 sets of cubic samples were printed on different processing parameters such as laser power (225W, 275W, 325W), scanning speed (800mm/s, 1100mm/s, 1400 mm/s), layer height (0.3mm) and hatching distance (0.10mm, 0.12mm, 0.14mm ). It was found that hardness of 383 - 448 HV was obtained where samples P3, P9 and P5 gave the highest, medium and lowest hardness values. Based on the microstructure observation, α + β phase and martensite structures are produced due to the vanadium content of 4% and heat treated at 935°C. A critical review was also studied to compare previous studies that used different holding times on SLM-printed Ti6Al4V 3D components. It was found that different holding times did not have a significant effect on the mechanical properties of Ti6Al4V 3D components where the outcome of previous studies alligns with that of from this study. In addition, past works have also reported that heat treatment is able to lower the residual stresses in SLM-printed Ti6Al4V 3D components. Finally, the effectiveness of heat treatment in reducing the residual stresses in SLM-printed Ti6Al4V 3D components at different printing parameters should also be studied to understand the mechanism of microstructural changes during and after heat treatment.

The Swelling–Shrinkage Properties of Intact and Disturbed Clayey and Marly Soils: The Density Effect

Expansive soils commonly encountered beneath foundations often lead to structural issues inducing expensive repairs. With the increase of the frequency of dry summers and irregular rainfall patterns, the clayey and marly soils become more and more sensitive to shrinking and swelling phenomena. So to find solutions and improve the knowledge on such phenomena especially in temperate countries where the saturation state is considered as the usual soil state, the impact of the soil density on shrinkage was studied by varying the compaction mode and introducing a swelling step before shrinkage. As expected, dynamically or statically compacted clayey or marly soils exhibited high shrinkage deformation when the soil had a low density. The swelling before shrinkage impacted the soil structure but ultimately had a low effect on shrinkage deformation. Swelling deformation was also influenced by density; the denser the soil, the more sensitive the compacted soil became to swelling. Furthermore, compaction modes induced differences in swelling or shrinkage amplitude that couldn’t be explained by microstructural observations. Finally, results demonstrated that intact soil behavior after shrinkage could be extrapolated from swelling–shrinkage tests conducted on remolded soil samples, thus decreasing the cost of field investigations.