Microstructure Mechanical Properties Research Articles

In-depth understanding in the effect of hydrogen on microstructural evolution, mechanical properties and fracture micro-mechanisms of advanced high-strength steels welded joints

The hydrogen embrittlement (HE) mechanism of QP980 steels laser welded joints with complex microstructures is unclear. The joint with hydrogen pre-charging fractured at the inter-critical heat affected zone (ICHAZ) in slow strain rate tensile test, and the relative loss of elongation amounted to 84.8%. Hydrogen-induced microcracks mainly initiated inside martensite (~ 60%). Hydrogen-induced crack propagation paths of the joints were transgranular propagation of martensite and intergranular propagation of ferrite/martensite interface. The HE mechanism of the joint was the combination of the effects in hydrogen-enhanced localized plasticity (HELP) and hydrogen-enhanced decohesion (HEDE).

The strengthening mechanism of mechanical and tribological properties of TiC-reinforced 316 L matrix composites fabricated by selective laser melting

Selective laser melting (SLM) has been proved to be a promising additive manufacturing technique to fabricate high-performance metal matrix composites (MMCs) with unique microstructures. In this study, TiC-reinforced 316L MMCs were successfully prepared by SLM. The effects of TiC addition on the microstructure evolution, mechanical properties and tribological behavior were systematically investigated to study the strengthening mechanism. The TiC/316L MMCs fabricated by SLM exhibited a high relative density of over 99.6% and were close to full density. The TiC particles are effectively bonded with the 316L matrix, serving as a means of dispersion strengthening. In addition, the grains were significantly refined, and the dislocation density was greatly enhanced with the addition of TiC particles, which reinforce the strength of the material. Tensile tests show that the tensile strength of TiC/316L MMCs increased by 49.9% from 707 to 1060MPa and yield strength increased by 44.2% from 543 to 783MPa with 4wt.% TiC. Besides, the tribological behavior of TiC/316L MMCs was much superior to the pure 316L. The findings provide a new perspective on ceramic particles reinforced stainless steel MMCs with tailored microstructure and excellence performance.

SiC nanoparticles additions to squeeze-cast Mg-5.0Al-2.0Ca-0.3Mn alloy: An evaluation of microstructure and mechanical properties

The influences of the SiC nanoparticles (SiCnp) content on the microstructural modification and mechanical properties of the squeeze-cast Mg-5.0Al-2.0Ca-0.3Mn (AXM520) alloy have been investigated. The concentrations of the SiCnp are varied from 0.5 to 3.0 (wt%), and the nanocomposites (NCs) are abbreviated as NC0.5SiC, NC1.0SiC, NC2.0SiC and NC3.0SiC. The as-cast microstructures of the AXM520 alloy and NCs consist of an α-Mg phase, a eutectic of α-Mg and (Mg,Al)2Ca (C36), and an Al8Mn5 phase. Additionally, the SiC phase is also present in the NCs. The continuous network of the C36 phase is fragmented and becomes discontinuous as the content of the SiCnp increases in the NCs. All the NCs exhibit superior tensile and compressive properties than the AXM520 alloy. The NC2.0SiC exhibits the best tensile properties among the NCs employed. The YS of the NCs improves with the increase in the SiCnp content up to 3.0 (wt%). The UTS and %El of the NCs increase up to 2.0SiCnp (wt%), and beyond that, the same declines owing to the agglomeration of the nanoparticles. The discontinuous network of the C36 phase in the NCs inhibits crack propagation, leading to their improved %El. All the NCs exhibit higher strain-hardening exponent (n) and strain-hardening rate (SHR) compared to the AXM520 alloy. The superior ‘n’ and SHR exhibited by the NCs were attributed to the grain refinement and dislocations generation. The strengthening from CTE mismatch contributes the most to the overall strengthening of the NCs. The ‘Zhang and Chen’ model is modified by introducing an agglomeration factor, and the predicted YS of the NCs matches pretty well with the experimentally obtained values.

Microstructure Characteristics and Mechanical Properties of γ-TiAl/Steel Joints with Different Laser Pulse Currents

Microstructure Characteristics and Mechanical Properties of γ-TiAl/Steel Joints with Different Laser Pulse Currents

Enhancing wear resistance of AZ61 alloy through friction stir processing: experimental study and prediction model

Abstract In this study, the friction stir technique is proposed to process AZ61 alloy and artificial neural network is built to predict and compare the experimental wear results. The effects of different processing parameters, including spindle speed (800–1200 rpm), travelling speed (05–15 mm/min), and depth of press (0.8-1.2 mm) on the microstructural evolution, mechanical properties and wear behaviour investigated. The grain size of the FSP1 samples found to be 14 ± 2 µm and shifting of peaks are observed in the X ray diffraction analysis chiefly due to texture development. As the spindle speed, travelling speed increases the surface roughness increases, it is observed that Ra – for FSP1 and FSP9 is found to be 68.4 nm and 116.3 nm respectively. Highest micro-hardness (113.36 Hv) values were observed for FSP1 sample and least is FSP9 sample (79. 51 Hv) and BM sample (65.92 Hv). Due to increased heat input into the processed regime, the hardness decreased as rotational and traveling speed increased, resulting in the development of coarse microstructure and a reduction in hardness. Based on wear results it has been observed that specimen FSP1 sample (0.003 g and 0.28) had the lowest weight loss and COF values compared to other FSP conditions. This is due to the combination of process parameters resulted in sufficient heat generation, grain refinement, and strain hardening of the stir zone, which enhanced the wear resistance of the specimen. Coefficient of friction is reduced to 0.28 from 0.68, and weight loss has been reduced to about 58% as compared to BM sample. This work shows that enhancing the wear resistance of magnesium alloys using friction stir processing is a successful approach.

Compositionally graded titanium to aluminum processed by laser powder bed fusion process: Microstructure evolution and mechanical properties

A compositionally graded Ti–Al alloy with a designed composition range from pure Ti to pure Al was successfully produced by a laser powder bed fusion (L-PBF) system equipped with two powder feeders. The compositionally graded Ti–Al profile is confirmed by scanning electron microscopy, X-ray diffraction analysis, electron backscatter diffraction microscopy, and transmission microscopy. The graded material is free of macro-horizontal cracks, but micro-cracks appear at the center of the sample. Varying the Ti and Al ratio along the build direction induces microstructural changes, transforming α+β-Ti into solid solution, creating intermetallics (Ti and Al), and yielding an Al phase with diverse morphologies. Additionally, the Ti–Al ratio's influence on microstructure formation and phase evolution results in varying mechanical properties among the graded material's layers. The results demonstrate that the L-PBF process can achieve continuous compositional grading of Ti–Al materials in a single run. Moreover, this study hold the potential to facilitate the design and production of numerous compositional variants for high entropy alloys and multi-materials, enabling future investigation into microstructural evolution, phase transformation, and physical and mechanical properties.

Investigation of Hydrogen Embrittlement Effect on Microstructure Mechanical Properties and Fracture of Low-Carbon Steels

Steel hydrogen embrittlement (HE), a complex and multifaceted issue, can lead to sudden and catastrophic failure, without significant plastic deformation, making it a critical concern in the industrial sector. The present investigation focuses on the evaluation of HE effects regarding microstructure, mechanical properties degradation and type of fracture of AISI 1010 low-carbon steel, after accelerated hydrogen cathodic charging. Hydrogen was diffused electrolytically in 0.2 Μ H2SO4 solution, containing 3g/L of NH4SCN, using a cathodic current density of 10 and 20 mA/cm2, for 6 and 18 h. Mechanical properties were investigated through slow-rate tensile tests, as well as Charpy V-notch (CVN) impact tests, to determine the value of fracture toughness, both in uncharged and electrochemically pre-charged specimens. Vickers microhardness tests were conducted on the cross-sections of the hydrogen charged samples to evaluate embrittlement susceptibility, due to the presence of dissolved hydrogen. The microstructure modification was carried out through light optical (LOM) and scanning electron microscopy (SEM), in conjunction with an energy-dispersive X-ray detector (EDS). Slow scan X-ray diffraction (SSXRD) was also conducted for crystal structure analysis. The microstructure analysis showed the presence of large amounts of secondary cracks and cavities into the steel matrix, due to hydrogen diffusion and its accumulation at various sites. Hydrogen charging caused a significant gradual elongation decrease of the parent material, from 25% to 6.73%, in case of embrittlement at 20 mA/cm2 for 18h. Accordingly, after 18 h of exposure, the impact energy decrement was determined at 31.5%, at a current density of 10 mA/cm2, whereas the corresponding reduction at 20 mA/cm2 reached 68%.

Microstructure Evolution and Mechanical Properties of Ti–6Al–4Zr–4Nb Alloys Fabricated by Spark Plasma Sintering (SPS)

AbstractThe near-α Ti–6Al–4Zr–4Nb (wt pct) alloy is a recently developed alloy with potential for aerospace applications. This study evaluates the microstructure and mechanical properties of Ti–6Al–4Zr–4Nb produced by spark plasma sintering (SPS). The SPS samples sintered in the α + β regions exhibited equiaxed α with a neighboring thin β phase. Above the β-transus temperature, the α/β lamellar structure formed, allowing control of the grain size (100 ~ 200 μm). The compressive strength and the creep property of the SPS samples were compared with the LBPDed and the forged samples. The compressive strength of the SPS sample was lower than that of the LPBFed sample but similar to the forged sample. The SPS samples exhibited longer creep rupture life (2220 hours) than LPBFed samples (1730 hours), but shorter than the forged sample (4109 hours). The creep deformation mechanism of the lamellar structure in the SPS sample was dislocation creep.

The effect of deformation temperature in metastable austenite zone on microstructure evolution, mechanical and corrosion properties of high Cr ferritic-martensitic steel

The effect of deformation temperature in metastable austenite zone on microstructure evolution, mechanical and corrosion properties of high Cr ferritic-martensitic steel

Study on microstructure and mechanical properties of 3003 aluminum alloy joints brazed with Al–Si–Cu–Ni paste brazing materials

Paste-type brazing materials have advantages such as adjusting the complexity of the parts to be soldered, easy storage and production in certain quantities. They can be used for brazing heat exchangers, liquid tanks and corrosion resistant parts. In this work, the microstructures and thermal behaviors of Al–Si–Cu–Ni brazing materials with different contents were investigated, and the effect of brazing process on the microstructural evolution and mechanical properties of brazed joints produced under nitrogen-filled environment was examined. It was found that the melting temperature of brazing material Al–5Si–20.5Cu–2Ni were ranged from 512.86 to 549.37 °C. The microstructure of Al–5Si–20.5Cu–2Ni consisted of α-Al solid solution, CuAl2 intermetallic compounds, the Al–Si–Cu phase, and some fine irregular Si particles in a homogenous manner. The microstructure of the brazed joints was uniformly formed during the brazing condition of 580 °C for 20 min, and the shear strength of the joints reached 41.76 MPa.

The Influence and Mechanism Analysis of the Longitudinal Magnetic Field on the Microstructure Evolution and Properties of AZ40 Welds

This paper studied the effect of the longitudinal magnetic field (LMF) on the microstructure evolution and mechanical properties of AZ40 argon tungsten arc welding joints. Magnetic field-assisted argon tungsten arc welding technology was used to achieve butt welding of an AZ40 Mg alloy sheet with a thickness of 1.5 mm. The microstructure of the Mg alloy weld was studied by using metallographic microscopy and scanning electron microscopy. Mechanical performance of the Mg alloy weld was evaluated by using a hardness tester and universal tensile machine. The experimental results revealed that the average crystallite dimension of the weld zone of the Mg alloy joint reached 43 μm without an LMF. By introducing LMF-assisted technology, the weld structure was significantly refined and the average crystallite dimension of the weld seam was reduced by 39.5% to 26 μm with a coil current of 1.2 A. For the joint without magnetic field assistance, the optimum tensile strength of the AZ40 weldment was 225 MPa under a welding current of 80 A, and fracture occurred in the center of joint welding seam. Under an LMF coil current of 1.2 A, the joint strength increased from the initial 225 MPa to 254 MPa, and fracture occurred at the weld edge with obvious plastic fracture characteristics. It can be confirmed that the LMF-assisted welding process effectively improved the microstructure characteristics of the weld seam and strengthened the microhardness and mechanical performance of the AZ40 joint.

Microstructure evolution and ductility improvement of additively manufactured biodegradable zinc–magnesium alloys via annealing

Zinc–magnesium (Zn–Mg) alloys, fabricated by laser powder bed fusion (LPBF) additive manufacturing techniques, have emerged as promising candidates for biomedical implants due to their biodegradation capability, superior mechanical strength, and excellent biocompatibility. However, LPBF-fabricated Zn–Mg alloys still face challenges related to extremely low ductility and limited exploration of degradation characteristics. In this study, the impact of Mg incorporation on the printability, degradation properties, microstructure, and mechanical properties of LPBF-fabricated Zn–Mg alloys was primarily investigated. Furthermore, we proposed a viable annealing post-processing route for the first time to tailor the microstructural characteristics of the fabricated Zn–Mg alloy and enhanced its limited ductility. The results demonstrated that by applying a laser power of 80 W and a scanning speed of 600 mm/s, the relative density of LPBF-fabricated Zn–Mg alloy reached 98.62%. Increasing the Mg amount from 1 to 5 wt% refined the grain size while promoting an increase in Mg2Zn11 and MgZn2 phases. Among these compositions, the Zn–1Mg alloy exhibited the greatest degradation rate at 0.126 mm/year. The annealing treatment facilitated the microstructure evolution of the Zn–1Mg alloy, resulting in equiaxed grains, increased average grain size, high-angle grain boundaries, and enrichment of Mg at grain boundaries. After annealing at 300°C for 0.5 h, the tensile strength of Zn– 1Mg alloy decreased from 254.92 to 170.93 MPa, while the elongation significantly increased by a factor of 14.3 from 0.55% to 8.43%. These findings provide valuable insights into an effective post-processing approach for tailoring the microstructure and resultant mechanical properties of LPBF-fabricated Zn and its alloys.

Microstructure Evolution and Mechanical Properties at Ambient and Elevated Temperatures of in-situ TiB2/2219Al Matrix Composites During Cold Rolling

Microstructure Evolution and Mechanical Properties at Ambient and Elevated Temperatures of in-situ TiB2/2219Al Matrix Composites During Cold Rolling

Influence of intermetallic phase (TiFe) on the microstructural evolution and mechanical properties of as-cast and quenched Ti–Mo–Fe alloys

This study presents the phase analysis, microstructural characteristics, and mechanical property evaluation of the as-cast and quenched Ti–15Mo–xFe alloys with high iron content ranging from 4 to 12 weight percent. All the four alloys were produced in a vacuum-arc melting furnace. Heat treatment in the form of solution treatment was performed in a muffle furnace at a temperature of 1100 °C, with 1-h holding time and the samples were rapidly quenched in ice-brine. X-ray diffractometer (XRD) was used to analyses the phases present in each alloy whereas the optical microscope (OM) was employed to track the microstructural evolution and percentage porosity. The mechanical properties of the alloys were evaluated using a tensile test and compression test method while the micro-Vickers hardness measurements were conducted to evaluate hardness of the alloys. The XRD patterns of as-cast showed peaks belonging to the β and α″ phases and intermetallic B2 TiFe phases. The as quenched XRD peaks illustrated β phase only and Fe·Ti·O2 phases. The as-cast OM micrographs revealed equiaxed β grains, substructures, dendritic structure, and pores forming around the grain boundaries. The quenched OM showed only β equiaxed grains with pores throughout the grain boundaries. The tensile properties such as ultimate tensile strength (UTS) and elastic modulus (E) of as-cast TMF0 were 264 MPa and 79 GPa respectively and these properties changed upon quenching to 411 MPa and 66 GPa respectively. The elastic modulus of TMF1 in as-cast condition was 74 GPa. The UTS and E of TMF1, TMF2, and TMF3 in as-cast and quenched conditions were not recorded due to the fragility of the samples that failed prior to yielding any useful data. The compressive strength in as-cast and in quenched condition decreased with an increase in Fe content. The micro-Vickers hardness in as-cast and quenched conditions showed a similar trend with hardness increasing slightly upon quenching for TMF0, TMF1, and TMF3 alloys but slightly decreased in the case of TMF2. The fracture surfaces of all the as-cast and quenched alloys were comprised of ductile and brittle fracture.

Achieving excellent strength–ductility combination of Al-aided Mg–Gd–Al–Zr–Zn alloys fabricated by cold metal transfer-based wire-arc directed energy deposition via uniform equiaxed grains and multiple precipitates

Limited ductility consistently poses a challenge for high-strength Mg–RE (rare earth) structures prepared by additive manufacturing. Particularly following heat treatment, while the strength of the Mg–RE alloy experiences a substantial increase, there is a noteworthy decrease in its ductility. Herein, a novel Mg–Gd–Al–Zr–Zn thin wall was successfully fabricated by cold metal transfer-based wire-arc directed energy deposition (CMT-WA-DED) and Al alloying. The microstructural evolution and mechanical properties of deposited and heat-treatment alloys were elucidated systematically. By adding Al element, Al2Gd and Al–Zr phases with thermal stability were precipitated in the deposited alloy. During the solidification or heat treatment stage, Al2Gd and Al–Zr phases could pin grain boundaries to restrict grain growth. The as-deposited alloys exhibited fully equiaxed grains at different heights and orientations. Thus, the thin wall exhibited good isotropic performance. After the heat treatment, the grain size only slightly grew and no abnormal grain growth was observed. Various morphologies of β precipitation phases were discovered along grain boundaries and within the grains. Additionally, a high density of β' and β1 phases within the grains and β phases along the grain boundary played pivotal roles in enhancing the mechanical strength of the Mg–Gd–Al–Zr–Zn alloy. The alloys exhibited an excellent combination of strength and ductility with ultimate tensile strength of 340 ± 7 MPa, yield strength of 212 ± 5 MPa, and elongation of 12.7 ± 0.9 %. This work provides theoretical and practical reference value for the Mg–RE structures obtaining an excellent combination of strength and ductility prepared by additive manufacturing.

A Study on the Microstructural Evolution, Interfacial Diffusion and Mechanical Properties of Ultra-thin Stainless Steel–Copper Composites Fabricated by Roll Bonding

A Study on the Microstructural Evolution, Interfacial Diffusion and Mechanical Properties of Ultra-thin Stainless Steel–Copper Composites Fabricated by Roll Bonding

Low-temperature direct diffusion bonding of Zr702 alloys via electric current assistance

Integrated zirconium (Zr) alloy fuel claddings require low-temperature and high-efficiency joining technologies for nuclear applications. However, conventional direct-joining technologies make it challenging to satisfy critical requirements at relatively low temperatures in a short time. As a promising alternative, the electric-current-assisted joining (ECAJ) method was studied to reduce the joining temperature and time required for the direct joining process. ECAJ was performed on a spark plasma sintering apparatus, with the specimens assembled with and without graphite dies in the two models. The microstructural evolution and mechanical properties of Zr/Zr joints were investigated at 600 − 900 °C for 1 s to 30 min under a pressure of 30 MPa using different configurations with or without a graphite die. While the joint quality varied with the joining conditions, no significant phase transformation, abnormal grain growth, or preferential orientation was observed at the interface. The maximum shear strength of 404 ± 78 MPa and hardness of 370.9 ± 49.8 HV were achieved at 600 °C for 10 min using a die-less configuration. The joining mechanism was discussed in terms of the potential thermal and electric effects inside the specimen, with the low-temperature joining mechanism attributed to the combined effect of transient overheating and electric-field-accelerated element self-diffusion at the interface, with the latter playing a leading role.

Effect of Cr content on microstructure, mechanical, and corrosion properties of CoCrxFeMnNi high-entropy alloys fabricated by selective laser melting

The method of using mixed powder for SLM in-situ alloying to prepare high entropy alloys has been verified to be feasible. In this investigation, the effect of Cr addition on microstructure uniformity, mechanical properties, and corrosion resistance of CoCrxFeMnNi High-entropy alloy (with x = 0.4, 0.7, 1.0, 1.3 at. %) prepared by the SLM in-situ alloying technique has been thoroughly investigated. X-ray diffraction and scanning electron microscopy suggest that all CoCrxFeMnNi HEAs samples are composed of a FCC matrix and little residual Cr particles, and all elements of the FCC matrix are evenly distributed, accompanied by a very small amount of Mn evaporation. Electrochemical corrosion tests have shown that with an increase in Cr content, the corrosion resistance of the alloy is significantly improved. The CoCr1.3FeMnNi HEAs possess the best corrosion resistance against the attack of the Cl ion, with a corrosion rate 0.671 × 10−3 mm / year. Furthermore, the Cr element can significantly improve the microhardness, tensile strength, and plasticity of CoCrxFeMnNi HEAs. The CoCr1.3FeMnNi HEAs possess the best mechanical properties, with microhardness 217.8 HV0.5, tensile strength 691 MPa and elongation rate 18.9%, respectively.

Effect of ageing temperature on the microstructural evolution and mechanical properties in M2C and NiAl co-precipitation secondary hardening ultrahigh-strength steel

A novel cost-effective secondary hardening ultrahigh-strength steel, strengthened by the co-precipitation of M2C and NiAl, was developed. The present study systematically investigated the co-precipitation evolution, austenite reversion, and mechanisms of strengthening and toughening at different ageing temperatures. As the ageing temperature increased, the quenched microstructure underwent various transformations, including precipitation and dissolution of cementite, nucleation and coarsening of M2C and NiAl nanoparticles, as well as reversion of austenite. At ageing temperatures of 427 °C and 454 °C, a small amount of cementite was present in the martensite matrix, and M2C and NiAl precipitates started to form, resulting in low strength and poor toughness. At 482 °C, the peak-ageing stage was reached, achieving a maximum yield strength of 1875 ± 4 MPa and an ultimate tensile strength of 2185 ± 3 MPa. This strength is primarily attributed to shear strengthening of NiAl particles and Orowan strengthening of M2C carbides. Additionally, the complete dissolution of cementite at this stage improved toughness. As the ageing temperature increased to 510 °C and 538 °C, the strength decreased due to coarsening of M2C, while the toughness improved as a result of film austenite reversion and enhanced dislocations bypassing around the M2C carbides.

Impact of in-process cooling and tool rotation speed on the mechanical and microstructural characteristics of friction stir processed AA2024

Despite significant grain size refinement, friction stir processing (FSP) of heat-treatable aluminum alloys is found to degrade the alloys of strength and hardness qualities. The drop in strength brought on by coarsening or the dissolution of the strengthening precipitate(s) could not be made up for by the improvement in strength brought about by the refinement of grain size following FSP. In order to get around this, the current work looks into a practical method of heat rejection from the FSP zone in addition to grain size refinement during FSP of AA2024 to regulate the precipitate evolution. Under natural cooling, air cooling, and CO2 cooling conditions, friction stir processing (FSP) was used to change the microstructure of Solutionized AA2024 at three distinct rotation speeds of 750, 1180, and 1500 rpm (fixed traverse speed of 50 mm/min). The microstructural evolution (through optical microscopy and SEM) and mechanical properties of FSP samples under different conditions of rotation speed and cooling and their differences were mainly discussed. All the FSP samples have a higher Vickers hardness than the base metal (minimum variation of 16.79% and maximum variation of 41.05%). The maximum hardness, yield strength, tensile strength, and elongation have been obtained under air cooling conditions and a rotation speed of 1180 rpm, which is a result of the simultaneous and effective effect of grain boundary strengthening and precipitation hardening.