Hardness Increment Research Articles

Influence of Deposition Parameters on Hardness Properties of InconelTM 718 Processed by Laser Powder Bed Fusion for Space Applications

InconelTM 718 is widely used for commercial application in aerospace industry and additive manufacturing process allows for versatile design and manufacturing opportunities. In the present research, the results of a wide experimental campaign run on additive manufactured InconelTM 718 specimens obtained with different processing parameters are presented. In particular, the influence of process parameters (for both vertical and horizontal planes with respect to the building direction) on the hardness properties are investigated. A further investigation is performed on the optimal hardness testing procedure for additive manufacturing. The research is extended to as-built and heat-treated specimens. The new insight gained is that the orientation of the printing direction with respect to indentation direction can be responsible for scattering in hardness measurements and indentation size effect. As-built specimens show a strong anisotropy for in-plane and growth directions and an increment of hardness with respect to increasing energy density. The difference between hardness value with respect to the energy density and the measurements scattering are reduced by the heat treatment. A careful handling of hardness data is required when dealing with additive manufactured materials.

Wear Evaluation of Copper-Nickel-Aluminum Alloys under Extreme Conditions

Cu-Ni-Al alloys at different concentrations were obtained using a high frequency induction melting unit, keeping a balance in the nominal compositions. Light alloys are important to be used in industrial applications. Aluminum additions result in a positive hardness increment of the ternary alloys in comparison with the binary Cu-Ni alloys. Generalized wear mechanisms of the alloys with low aluminum content are basically type abrasive, while samples with 5 and 10 at.% Al present an oxidative-adhesive wear mechanism. Wear results have indicated that aluminum addition affects positively the wear resistance, mainly in samples with high aluminum content product of the creation during the test of different oxides corresponding to the elements present in the alloys.

In-situ formation of Al3Ni nano particles in synthesis of Al 7075 alloy by friction stir processing with Ni powder addition

Bulk aluminum 7075 alloy strengthened by nano-sized Al-Ni intermetallic particles is synthesized by friction stir processing (FSP). Al 7075 alloy powders mixed with 10 wt% Ni nano powders were used as feedstock. The extensive thermal-mechanical actions by FSP accelerate the reaction and inter-diffusion between Al 7075 powder particles and Ni nano powder particles, resulting in the formation of Al 3 Ni nano particles, in-situ during FSP, confirmed by scanning electron microscopy and X-ray diffraction. The presence of the Al 3 Ni nano particles in the Al 7075 matrix increases the micro hardness by 19.0% and 14.6%, respectively, under as-processed and T6 aged conditions, compared to the one synthesized by FSP from 100% 7075 alloy powder. The hardness increment agrees with the estimation from the Orowan strengthening effect of the Al 3 Ni reinforcement. Furthermore, Al 7075 alloy with in-situ formed Al 3 Ni shows a tendency of promoting T-Al 2 Mg 3 Zn 3 and inhibiting η-MgZn 2 precipitation during post synthesis heat treatment between 50-500°C. This work suggests the potential of FSP as an effective process to bulk synthesize Al alloys with in-situ formation of Al 3 Ni nano particles to further enhance the properties.

On the control of nanoprecipitation in directly aged Alloy 718 via hot deformation parameters

Alloy 718 remains the material of choice for critical parts in next-generation aircraft engines. The direct ageing (DA) route is known to significantly change the final multi-scale microstructure, achieving superior yield strength. This includes changes in the dislocation density and co-precipitation behaviour, although a systematic study of the influence of forging temperature and strain rate is currently unavailable. Here, we elucidate how geometrically necessary dislocations (GNDs) generated during hot deformation impact the morphology and co-precipitation of γ′ and γ′′ during ageing. Lower GND density at high-temperature forging leads to increased formation of γ′′ monoliths and up to two-fold hardness increments after ageing. For all selected forging temperatures, the high GND density at the intermediate strain rate of 1 s − 1 generates ∼8% lower fractions of duplet co-precipitates, minimizing DA hardness increments. Understanding the inverse correlation between GND density and DA efficiency is essential for designing Alloy 718 for next-generation aerospace applications.

Hybridized-flow flame spray (HFFS) process for the development of superior ceramic coatings

The present study deals with a novel, effective and single step thermal spray coating process development. The process is named as ‘Hybridized-Flow Flame Spray (HFFS) process’. The process is very much suitable for the development of ceramic coatings with superior properties when compared to conventional Powder Flame Spray (PFS) coatings. The HFFS process is capable in addressing the shortcomings (porosity, density, hardness, surface quality) of PFS coatings. The physical, mechanical and metallurgical analysis of PFS and HFFS coatings are done using density measurement kit, 3-D optical profilometer, Vickers and scratch hardness, and scanning electron microscope (SEM). The results show significant improvement in the properties. The increment in density (≈24%), hardness (Vickers ≈ 37% and scratch ≈ 126%); and decrement in coating thickness (≈35%) and average surface roughness (≈47%) of HFFS sprayed coatings are observed. The results are benchmarked with those of PFS coatings. The improved responses are attributed to the densification of coating structure and improved microstructural changes due to the presence of hybridized flow in the HFFS.

Enhanced mechanical properties and thermal stability in additively manufactured Al-Ni alloy by Sc addition

The trade-off between printability and performance of Al–Ni–Sc alloy fabricated by additive manufacturing (AM) herein is demonstrated. By designing eutectic solidification, a crack-free microstructure was obtained. Extremely high cooling rate during rapid solidification promoted the formation of spherical Al3Ni nano-particles. Further by adding Sc, coherent L12 Al3Sc nano-particles were formed, which served as nucleation sites of α-Al to transform columnar grains into equiaxed grains and provided further strengthening. Superior mechanical properties with tensile strength of 445 MPa and yield strength of 320 MPa at ambient temperature were obtained. And this Al–Ni–Sc alloy can still exhibit excellent tensile strength of 259 MPa and yield strength of 248 MPa at 250 ℃. After thermal exposure at 200–400 °C, Al–Ni–Sc alloy consistently showed higher microhardness than the corresponding Al–Ni alloy and both alloys retained hardness at 300 °C for 50 h. The Al3Sc nano-precipitates provided additional hardness increments and compensated the microhardness decrease owing to the coarsening of Al3Ni nano-particles during high-temperature exposure. The coarsening process studied on Al–Ni alloy can be divided into two stages, rapid coarsening stage at first 0.5 h due to solute supersaturation and coarsening slowing stage due to the decreased coarsening drive. Following the classical coarsening mechanism–LSW model and Arrhenius equation, the corresponding diffusion activation energy of the second stage was calculated to be 23.03 KJ/mol, much lower than Ni self-diffusion in Al. This phenomenon was attributed to the formation of numerous defects and grain boundaries during AM as fast diffusion channels of atoms. The finding of this work provides guidance for considering discrepancy of Al alloys produced by AM and cast.

Influence of graphite particles in UV-curable corrosion protection coating from palm oil based urethane acrylate (POBUA)

Replacing petroleum oil with renewable sources from natural oil in producing polymer coating is being widely attracting many researchers and inventors. In this study, palm oil-based urethane acrylate (POBUA) coating was developed as a protective coating for mild steel by using the ultraviolet irradiation technique. The POBUA was synthesized by reacting acrylated palm oil and isocyanate via in situ intercalative polymerizations with the presence of hydroxyethyl acrylate and 4 methoxy phenol (4mph). Different loadings of graphite particles (0.1 wt%, 0.5 wt% and 0.8 wt%) were introduced into the POBUA with the presence of Irgacure 184 as the photoinitiator. The formulated coating resin was applied on the mild steel substrates and the overall performances were investigated using Fourier transform infrared spectroscopy , contact angle measurements, X-Ray Diffraction, thermogravimetric analysis, electrochemical impedance spectroscopy , and Field Emission Scanning Electron Microscopy . Meanwhile, Gel content extraction and Pendulum Hardness were done on the cured film to investigate the performance of the polymerized coating polymer. The obtained results exposed good distribution of graphite particles in the POBUA polymeric matrix will influence the overall performance of the POBUA coatings at POBUA + 0.5 wt% graphite. Infrared spectrum demonstrated the formation of the crosslinked network was not disrupted with the addition of graphite particles, while increment of crystallinity index and hardness observed. Meanwhile TAFEL polarization elucidate the present of graphite particles reduced the curable POBUA coating corrosion current density from 102.6 × 10 −6 to 27.3 × 10 −12 Acm −2 with decreasing of mild steel corrosion rate per year from 31.24mpy to 125.1 × 10 −6 mpy. However, morphology showed that the addition of high graphite content (0.8 wt%) increased the tendency to particles agglomeration. Nevertheless, the results obtained showed that the presence of graphite particles in POBUA is beneficial in improving the strength of the coating against surface degradation and corrosion. This research demonstrates that POBUA/Graphite curable coating has a good potential application in mild steel protection. • Anticorrosion study for palm oil-based urethane acrylate enhanced by graphite was carried out. • Graphite particles influences the corrosion behavior as shown in Tafel plot. • The strength of the coating against corrosion was enhanced with the presence of graphite. • Graphite particles enhanced charge transfer resistance R ct of POBUA. • The POBUA R ct increased from 0.92 × 10 6 Ω up to 9.253 × 10 6 Ω.

Tribological Characteristics of High-Chromium Based Multi-Component White Cast Irons

It has been evaluated the relationship between the microstructure and three-body abrasive wear behavior of high-chromium (18 and 27 mass % Cr) based (3 mass % each of V, Mo, W, and Co) multicomponent white cast iron materials (high-Cr MWCIs). It was also compared to MWCI to determine the service life of the materials. The results indicate that the microstructure of the material is composed of mainly martensite matrix and different types of precipitated carbides. The wear resistances of both the high-Cr MWCIs are higher than MWCI owing to the higher hardness (4–18% increment in hardness), although they contain fewer carbide types. The carbide volume fraction of high-Cr MWCI increases with increase in the Cr content, but the hardness decreases, leading to a reduction in wear resistance. This is because the transition metal significantly consumes C atoms to form more eutectic carbides during solidification, which is exacerbated by the depletion of C in the matrix during heat treatment to form coarser secondary carbides. This means that increasing the addition of Cr does not always lead to an increase in the hardness or wear resistance of the material. In addition, the wear resistance of 27Cr MWCI after tempering (wear rate: 8.80 × 10−5 g/m) is higher than that after quenching (wear rate: 9.25 × 10−5 g/m) owing to the increase in the fracture toughness of M7C3 carbide. This is contrary to the case of 18Cr-MWCI; the wear resistance after tempering (wear rate: 5.29 × 10−5 g/m) is worse than that after quenching (wear rate: 5.11 × 10−5 g/m) owing to the reduction in hardness as a stress-relieving effect.

Investigation on Mechanical Behaviour of LM6 Aluminum Alloy Hybrid Composites Processed Using Stir Casting Process

The stir casting process produces boron nitride (B4N) and fly ash-based LM6 metal matrix composites. This hybrid composite was fabricated by varying fly ash from 3% to 15% with an increase of 3%. While the other reinforcement B4N concentration was kept constant as 3%. The morphology of the metal matrix composite is analysed using a light optical microscope. The microstructure analysis shows the uniform distribution of hybrid reinforcement throughout the matrix, and only a few clusters are found in the matrix alloyed with 15% B2N. Both pure and reinforced matrices are evaluated for the mechanical properties’ evaluation. The result shows an increment in hardness from 70.4 VHN to 96.2 VHN. Similarly, the tensile strength of the composite material is improved from 151 MPa to 192 MPa. The reason for improving strength and hardness is the uniform distribution of hybrid reinforcement in the LM6 matrix.

Evaluation of radiation resistance of an austenitic stainless steel with nanosized carbide precipitates using heavy ion irradiation at 200 dpa

Despite many advantages as structural materials, austenitic stainless steels (SSs) have been avoided in many next generation nuclear systems due to poor void swelling resistance. In this paper, we report the results of heavy ion irradiation to the recently developed advanced radiation resistant austenitic SS (ARES-6P) with nanosized NbC precipitates. Heavy ion irradiation was performed at high temperatures (500 °C and 575 °C) to the damage level of ∼200 displacement per atom (dpa). The measured void swelling of ARES-6P was 2–3%, which was considerably less compared to commercial 316 SS and comparable to ferritic martensitic steels. In addition, increment of hardness measured by nano-indentation was much smaller for ARES-6P compared to 316 SS. Though some nanosized NbC precipitates were dissociated under relatively high dose rate (∼5.0 × 10−4 dpa/s), sufficient number of NbC precipitates remained to act as sink sites for the point defects, resulting in such superior radiation resistance.

Microstructure evolution and mechanical response of a boron-modified Ti–6Al–4V alloy during high-pressure torsion processing

Research was conducted on the microstructural evolution and ensuing mechanical response from high-pressure torsion (HPT) processing of Ti–6Al–4V alloy in the as-cast and β-forged conditions with and without 0.1 wt% boron addition. The boron addition produces refinement of the prior β grains and the (α+β) colonies and introduces an additional TiB phase but this affects the deformation response and the microstructural evolution only at low strains of 0.5–5 rotations. In the initial condition the orientation of the (α+β) colonies significantly affects the deformation response and leads to differences in substructure formation in both the as-cast and β-forged conditions. This orientation dependence counts on the initial microstructural differences between the unmodified and the boron modified alloys. At higher strains, there is a similar deformation response and microstructure evolution for all the alloys. The hardness variation with equivalent strain is similar for the unmodified and boron modified alloys in as-cast and β-forged conditions and represents various deformation regimes in HPT-processing. Strength modelling confirms a simultaneous contribution from microstructural refinement and increased dislocation density towards the hardness increment during HPT processing. Overall, the as-cast and β-forged Ti–6Al–4V-0.1B alloys possess identical deformation response to the β-forged unmodified Ti–6Al–4V alloy in the initial and intermediate stages. At high levels of straining, all alloys respond in an equivalent manner, thus ruling out any possible effects from additional TiB phase or microstructural refinement for the boron-modified alloys.

Microstructure and mechanical property evolution of He-implanted nanochannel W film under post-annealing

Tungsten (W) has been selected as the most promising Plasma Facing materials (PMFs) due to its excellent properties. One of the most challenged problems for W is the He retention. Nowaday, a nanochannel structure film was presented to improve the He irradiation resistance of W. In this work, the microstructure and mechanical property evolution of He-implanted nanochannel W film under post-annealing from 573 to 1273 K were studied. A significant growth of He bubbles and the formation of large size holes at grain boundaries (GBs) were observed after post-annealing at 1273 K. In addition, a formation model of pores structure on surface caused by high energy He implantation was proposed. Moreover, a mitigated lattice swelling was observed at 1273 K due to the He-V clusters and He bubbles migration and coarsening. The shape of the He bubbles at 1273 K was also investigated in detail. The nanochannel film has a better resistance to the degradation of Young's modulus under the He implantation than compact film, due to the loose nanochannel. Hardness increment induced by the implantation of He was analyzed. The hardening effect of the He-implanted film annealing at 1073 K, resulting from the transition of He-V clusters or He bubbles distributions from dislocations to distributed vacancies, should be notice. Finally, the holes at GBs led to the decrease of both Young's modulus and hardness.

Effects of Glucose and Homogenization Treatment on the Quality of Liquid Whole Eggs.

To investigate the effect of glucose on the protein structure, physicochemical and processing properties of liquid whole eggs (LWE) under homogenization, different concentrations of glucose (0.01, 0.02, 0.04, 0.08 g/mL) were added into LWE, followed by homogenizing at different pressures (5, 10, 20, 40 MPa), respectively. It was shown that the particle size and turbidity of LWE increased with the increase in glucose concentration while decreasing with the increase in homogenization pressure. The protein unfolding was increased at a low concentration of glucose combined with homogenization, indicating a 40.33 ± 5.57% and 165.72 ± 33.57% increase in the fluorescence intensity and surface hydrophobicity under the condition of 0.02 g/mL glucose at 20 MPa, respectively. Moreover, the remarkable increments in foaming capacity, emulsifying capacity, and gel hardness of 47.57 ± 5.1%, 66.79 ± 9.55%, and 52.11 ± 9.83% were recorded under the condition of 0.02 g/mL glucose at 20 MPa, 0.04 g/mL glucose at 20 MPa, and 0.02 g/mL glucose at 40 MPa, respectively. Reasonably, glucose could improve the processing properties of LWE under homogenization, and 0.02 g/mL–0.04 g/mL and 20–40 MPa were the optimal glucose concentration and homogenization pressure. This study could contribute to the production of high-performance and stable quality of LWE.

Quantification of room temperature strengthening of laser shock peened Ni-based superalloy using synchrotron microdiffraction

Laser shock peening (LSP), a surface modification technique, is promising to enhance the strength and wear resistance for Ni-based superalloys. To understand the strengthening mechanism in a laser shock peened Ni-based superalloy DZ417G, we utilize synchrotron poly- and monochromatic X-ray microdiffraction, as well as electron microscopy and microhardness to quantify the local microstructures and mechanical properties at various depths. In the 1.2-mm-deep hardened layer, the microhardness increases monotonically by ∼50% from the unaffected interior to the surface. Quantitative microdiffraction analysis shows that large amounts of dislocations are introduced by LSP. High densities of 7.1 × 1015 m−2 and 11.8 × 1015 m−2 are seen close to the peened surface for the γ- and γ′-phases, respectively, which are 5 and 20 times of those in the unaffected region. Different gradients of dislocation density are observed for the two phases from interior to surface, and their combined effect accounts well for the hardness increment. Due to the unaltered γ′-precipitates and chemical composition in the LSP affected zone, the large density of dislocations dominates the observed strengthening. Combined poly- and monochromatic X-ray microdiffraction allows quantifying the local microstructures of plastic deformation over a large sampling scale that can hardly be achieved using other materials characterization techniques.

Flank Surface Treatment of Spur Gears Machined by MQL Assisted Hobbing Using Micro-Plasma Transferred Arc

In the present study, feasibility of micro-plasma transferred arc (M-PTA) for flank surface treatment of gears has been explored. 20MnCr5 spur gears manufactured by sustainable technique minimum quantity lubrication assisted hobbing (MQLAH) were subjected to M-PTA-based heat treatment for further improving the surface properties of flank surface and comparisons were made with respect to M-PTA treated gears machined by conventional flood lubrication assisted hobbing (FLAH). The results revealed that M-PTA enhanced flank surface hardness of all the gears without deteriorating the gear accuracy. However, flank hardness increment was observed to be almost 18% in case of MQLAH gears as compared to 15% for FLAH gears. This study proves that M-PTA based heat treatment after MQLAHcan result in superior surface hardness along with better gear accuracy and can improve the sustainability of overall process chain involved in machining-based gear manufacturing.

Fabrication, microstructural characterization and finite element analysis of functionally graded Al-Al2O3 disk using powder metallurgy technique

In the present work, powder metallurgy technique was employed to fabricate a three-layer functionally graded (FG) disk. The volume fraction of metal-ceramic composition changes radially as layer-1 (100 % Al), layer-2 (95 %Al +5 % Al2O3), and layer-3 (90 %Al +10 % Al2O3). The microstructural investigation was carried out under an optical microscope and SEM (scanning electron microscopy) integrated with EDS, confirming a uniform distribution of reinforcement particles (alumina) in the matrix (aluminum). Interface microstructure indicates a successful fabrication of FGM (functionally graded material) as the transition is uniform in the graded layer without the development of any crack or void at the interface. In comparison to layer-1, the average increase in hardness values was found to be 18 % and 29 % for layer-2 and layer-3 respectively. An increment in hardness was observed in layers where alumina composition is higher. The Archimedes principle was employed to calculate the experimental density of the sample, and the theoretical models were presented to effectively estimate the density of porous FG materials. Furthermore, theoretical models for estimating material properties such as Young's modulus and yield strength of individual layers were proposed on the basis of material composition and particle shapes obtained from the microstructure of FG disk. These material properties were then used in finite element formulation for the application of rotating disk, the validation of which is also proposed. Subsequently, finite element analysis was employed to perform stress analysis on layered FG disk when subjected to centrifugal loading.

Recent advances in experimental and molecular dynamics study of graphene-oxide/natural rubber composites: A review

Rubber nanocomposites are being studied because of their unique characteristics. Fillers are used in rubbers and elastomers to increase certain qualities for their ultimate uses. Fillers are used to strengthen rubber such as graphene/graphene oxide for the majority of activities. The hardness, modulus, anti-ageing and gas barrier properties of nanofilled-reinforced rubber are greater than pristine rubber. Studies from the literature depicted 150% increment in elastic modulus, 27.6% increment in modulus of rigidity and 35% increment in hardness of nitrile butadiene rubber when reinforced with graphene oxide (GO). Bulk, shear and Young’s modulus of vulcanised rubber rises by 19.13%, 21.11% and 26.89% when infused with carbon nanotube. Because of its unique electrical, thermal and mechanical characteristics, rubber nanocomposites loaded with GO are also in high demand in industrial applications. Rubber nanocomposites, different nanofillers like graphene and graphene oxide and their benefits have been discussed. The review also outlines the rubber/GO nanocomposites' production procedures, novel characteristics and possible uses.

Characterization of microstructure and hardening of SLM nickel-based alloy irradiated by He ions

For the application of additively manufactured nickel-based alloys in molten salt reactors (MSRs), it is crucial to evaluate their performance in nuclear environments, especially under He-induced damage. Therefore, in this study, the irradiation damage behaviour of selective laser melted (SLM) nickel-based GH3536 alloy was studied by irradiating it with He ions at various doses. Traditionally manufactured (TM) materials were used as reference materials to evaluate the resistance of SLM GH3536 to irradiation. Transmission electron microscopy (TEM) was performed to reveal the depth distribution of irradiation-induced He bubbles, as well as the characteristics of dislocation loops, using both on-zone scanning transmission electron microscopy (STEM) and rel-rod modes. Nanoindentation tests were performed on both alloys to investigate their irradiation hardening. The TEM graphs and quantitative analysis showed that, owing to the cellular sub-grain structures, the He bubbles in the SLM alloy exhibited a lower number density but larger size than those in the TM alloy. Additionally, the SLM alloy showed inferior He tolerance but better resistance to irradiation hardening, as revealed by the nanoindentation test results. Consistency between the experimental hardness increment and calculated yield stress increment showed that the irradiation hardening of the sample was mainly caused by the presence of irradiation-induced defects. A comparison between the on-zone STEM and rel-rod modes suggested that the rel-rod mode is more effective if only the effect of irradiation-induced defects on mechanical properties is studied. Furthermore, this study provides insight into the design of SLM nickel-based alloys for nuclear industry applications.

Fabrication and performance examination on explosively welded ODS-Cu / 316 L clad plate for CFETR divertor heat sink

Copper alloys are among the most promising candidate materials for divertor heat sinks owing to their remarkable advantages. However, it is challenging to use CuCrZr alloys as heat sink materials because of the harsh loading environment expected for plasma-facing components (PFCs) in future fusion reactors. Explosive welding is an effective method for manufacturing high-quality oxide dispersion strengthened copper (ODS-Cu) / 316 L stainless steel (SS) clad plates. Non-destructive testing results revealed a soundness bonding interface between ODS-Cu and 316 L without any detectable defects or cracks. In this study, optical microscopy and scanning electron microscope analysis revealed that the bonding interface did not contain any cavities and a typical wave-bonding morphology was observed. Moreover, the tensile stress of the bonding interface was higher than that of the ODS-Cu parent metal, and there was an increment in hardness on both sides near the bonding interface. The helium leak testing results indicate that the welded ODS-Cu / 316 L exhibits soundness without deformation or leakage at cyclic room and high temperatures. The results prove that the explosive welding method is a practical method for manufacturing high-quality ODS-Cu / 316 L clad plate that meet the design requirements and can provide critical references for the engineering design of the China Fusion Engineering Test Reactor (CFETR) divertor heat sink.

Optimization of precipitate hardening parameters of 7075 aluminum alloy using response surface methodology

In the present research work, combination of artificial aging (pre and post) and natural aging was performed on 7075 Al alloy. Aging parameters were optimized using response surface methodology model to get the maximum value of Vickers micro-hardness, hardness value, and tensile strength. Three factors with five levels each were used to develop the center composite rotatable design (CCRD-approach). The three factors were pre-artificial aging temperature, natural aging time, and post-artificial aging temperature. The contour plots, surface plots, and mean effects plots were drawn to study the effect of individual factors and interactions of the factors on micro hardness. The coefficient of the regression R2 was 0.9962 which shows the excellent accuracy of the developed model. One hundred and fifty-one percent increment in the micro hardness and 115% increment in the value of the ultimate tensile strength were observed in optimized sample compared to annealed sample. The Vickers micro-hardness, optical microstructural, tensile test, X-ray diffraction analysis, energy dispersive X-ray spectroscopy analysis, and fractography using scanning electron microscopy of fractured tensile specimen were conducted in this research work.