Microstructure Of Alloy Research Articles

Effect of Simultaneous Mg and Zn Addition on the Solidification and Microstructure of Multi-Element Hypoeutectic Al-Si Alloys

Effect of Simultaneous Mg and Zn Addition on the Solidification and Microstructure of Multi-Element Hypoeutectic Al-Si Alloys

Effect of the conventional shot peening and multiple shot peening on microstructure and residual stress of TC17 titanium alloy

This study examines the residual stress, microstructure, and stress-induced phase transformation of TC17 titanium alloy after different shot peening processes. A comprehensive analysis of the unique impact of shot peening on α-Ti and β-Ti was performed. The results indicate a substantial reduction in the grain size of the deformed layer and the creation of a high density of dislocations. Additionally, increased peening intensity results in decreased grain size, and multiple shot peening promotes further reduction in grain size. Compressive residual stresses were detected in the deformed layer, and multiple shot peening significantly augmented the residual stresses in the surface and near-surface regions. In particular, the highest compressive residual stresses after triple shot peening treatments were measured at −1079 MPa (at a depth of 10 μm for α-Ti) and −792 MPa (at a depth of 50 μm for β-Ti). In addition, multiple shot peening can significantly reduce surface roughness and enhance surface nanocrystallization when approximate surface residual stresses are obtained. Remarkably, the use of single shot peening revealed parallel stacking faults in certain α-Ti samples. However, under multiple shot peening, these stacking faults evolved into face-centered cubic Ti (FCC-Ti) with broader widths and a greater number. The stress-induced phase transition orientation relation was determined to be (0001)HCP//(11¯1)FCC and [21¯1¯0]HCP//[011]FCC, with α-Ti grains being interspersed with FCC-Ti, thus promoting additional grain refinement.

Oxidation and compositional modulation in single phase C14 Zr0.6Ti0.4Fe1Cr1 alloy

This study investigates the effects of heat treatment on the crystal structure and hydrogen absorption behavior of the AB2 type metal hydride Zr0.6Ti0.4Fe1Cr1. The objective is to understand how 3- and 6-day heat treatments at 1000°C influence the alloy's microstructure and hydrogenation properties. Using electron microscopy, EBSD analysis, X-ray diffraction, and hydrogenation measurements, we found that the as-cast alloy exhibits rapid hydrogen absorption with significant compositional variations due to segregation during casting, confirmed by a single C14 Laves phase in XRD. Heat treatment slowed hydrogen absorption and reduced hydrogen capacity, with XRD indicating the structure remained primarily C14 Laves phase. However, SEM/EDS analysis showed substantial microstructural changes, including the emergence of new phases and segregation of Zr-rich phases, likely non-hydride forming, influenced by elevated oxygen content. These new phases probably contribute to the reduced hydrogen uptake capacity.

Effect of brass slag particles on the microstructure and hardness of Al-Si alloy matrix composites

The current study investigated the effects of brass slag particles on the microstructure and hardness of Al-Si alloy (LM30) matrix composite. Stir casting was used to fabricate a composite with brass slag particles of finesize (i.e. 100–215 μm), coarse size(i.e. 215–350 μm) and three different concentrations of 3 wt%, 6 wt%, and 9 wt%. The dynamic shear force generated by stirring prevents brass slag particles from sinking into the melt which result in uniform particle dispersion throughout the melt. Optical microscopy analysis reveals a uniform distribution of reinforcement particles in cast composites, accompanied by silicon refinement. The findings suggest that the incorporation of industrial waste (brass slag as a reinforcement) in the fabrication process enhances microstructure and mechanical characteristics of composites. 9 wt% concentration of brass slag reinforced of fine size composite demonstrated an impressive ∼60.7% improvement in hardness compared to base alloy (LM30). It was also observed that theoretical density (ρth) and experimental densities (ρex) approximately 25% and 18.4% greater than that of the base alloy (LM30).

Microstructure, hydrogen storage properties, and thermodynamic characterization of ball-milled Mg90Ni5Y5 alloy

The hydrogen storage properties of the Mg90Ni5Y5 alloy were studied, which was prepared by vacuum electromagnetic induction melting and ball milling. The microstructure and phase evolution of the ball-milled alloys during the process of hydrogen absorption and desorption were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray diffraction (XRD). The alloys hydrogen storage properties were measured by semi-automatic Sievert instrument. Results show that the hydrogenated sample was composed of MgH2, Mg2NiH4 and YH3 phases. After dehydrogenation, Mg2NiH4 and MgH2 phases were completely decomposed, and YH3 could only be decomposed into YH2. After 2 cycles of adsorption dehydrogenation, the alloy was completely activated, and the maximum hydrogen desorption capacity was about 5.1 wt %. According to the Arrhenius equation, the ball-milled alloy activation energy of the dehydrogenation reaction of is only 75.7 kJ/mol.

Strain path dependent dynamic recrystallization and its resulted material flow and microstructure evolution of a titanium alloy

Changing strain path is an effective method to optimize the hot working process and improve microstructure and mechanical performance of titanium alloys. In this work, dynamic recrystallization (DRX) and its resulted material flow and microstructural behaviors in monotonic torsion (MT) and forward-reverse torsion (FRT) were comparatively explored by experimental and crystal plastic finite element simulation methods. The results indicate that both MT and FRT can induce discontinuous DRX (DDRX) and continuous DRX (CDRX). However, compared to MT where CDRX always prevails, FRT makes DDRX more important since it inhibits CDRX by recovering the lattice rotation during the reversal stage. Moreover, in FRT, the driving force and the grain boundary content for DDRX nucleation and bulging are relatively low at a small total strain. And the recovery of lattice rotation in FRT can also suppress CDRX. Therefore, DRX kinetics is obviously delayed at a smaller strain. As strain increases, both the stored energy for DDRX and the long-range misorientation gradient for CDRX are gradually greater, thus improve DRX kinetics. With these effects by DRX, although FRT exhibits a lower grain refinement degree at a smaller total strain compared to MT, it can make grain refinement degree rapidly rise and even close to that in MT at a greater strain. Also, FRT can obviously weaken the deformation texture by inducing extensive DDRX grains and recovering the lattice rotation of retained grains. In addition, the texture formed in forward stage and DRX delaying can result in a decrease in yield strength and softening rate in reversal stage, respectively, i.e., exhibiting remarkable Bauschinger effect, especially at a higher forward strain. These results can provide a basic guidance for designing the hot working process of titanium alloys to obtaining more refined microstructure and excellent properties of the components.

Aqua jet integrated fiber laser machining of quaternary NiTiCuZr alloy

ABSTRACT Low thermal diffusivity of NiTi-based smart alloy results in concentrated heat accumulation during laser beam machining which rises to adverse thermal effects like heat-affected zones, residual stresses, and alterations in microstructure of shape memory alloy (SMA) system. The addition of Cu and Zr can reduce the thermal hysteresis in the phase transformation of NiTi SMAs. Minimizing thermal hysteresis is desirable in SMA applications where precise control of the phase transformation temperatures is required, such as in actuators, sensors, and medical devices. Therefore, aqua jet integrated laser (AJ-FLBM) machining is a suitable choice for smart materials that need to be machined with high precision and low heat affected zone. In this current research, the NiTiCuZr SMA is machined using AJ-FLBM to investigate the effects of process variables on surface characteristics measured using RSM-BBD approach. The surface quality was enhanced by 68.93% with a gradual decrease in laser power (P), cutting speed (CS), and an increase in frequency (F). Aqua jet integrated FLBM technique may reduce heat affected zone due to the removal of heat in areas near the cutting location. This was confirmed by the DSC test which reveals that optimal machining inputs do not alter shape memory properties.

The effect of well temperature on the microstructure and the mechanical performance of bismuth-based plugs in well plugging and abandonment operations

Bismuth-tin (BiSn) alloys are considered promising candidates as potential alternatives to cement for well plugging and abandonment (P&A) applications to prevent any uncontrolled flow of deep reservoir fluids to the surface. As the temperature in the well varies with depth, the final microstructure of the BiSn alloy after its solidification might be influenced, and consequently the mechanical performance of the alloy will also be affected. The aim of this study is to evaluate the microstructural evolution of the BiSn alloy after solidification, at temperatures between 20 °C and 90 °C, to reflect in situ conditions from approximately 800m to 3 km depth. Microstructural characterization was carried out by using scanning electron microscopy (SEM) and electron backscatter diffraction (EBSD). The microstructural analysis revealed that the plug subjected to the lower temperature resulted in finer microstructure, whereas the grain size of the material was increased at higher temperatures. Additionally, the theoretical lever rule was employed to validate the microstructural findings. The observed microstructures were also correlated with tensile tests, which showed that the plug at 20 oC had a yield strength of 67,25 MPa, whereas the yield strength of the plug at 90 oC was only 41,64 MPa. In addition, hydraulic push-out tests further confirmed that lower testing temperatures correlate with higher pressure tolerance of the plug. The plug at 20 oC could withstand 113,5 bar, compared to the plugs at 60 oC and 90 oC which could withstand 90,4 and 50,9 bar, respectively. From all the experimental tests conducted, the outcome was that the lower temperature of 20 oC resulted in a material with a finer microstructure, which plays an important role in enhancing the mechanical properties of the bismuth-based plug. This study aims to advance the understanding of BiSn alloy performance in plug and abandonment (P&A) operations, thereby supporting the industry's efforts to qualify BiSn alloys as effective well-barrier materials.

Optimization design and interface characteristics research of high damping NiTi - Nickel-Aluminum Bronze functional gradient composite coating additively manufactured by high-speed laser-directed energy deposition

The near-equatomic NiTi shape memory alloy demonstrates exceptional damping performance due to its distinctive low-temperature self-cooperative martensitic internal friction. This study successfully fabricated NiTi-NAB (Nickel-Aluminium bronze shape memory alloy) functionally graded composite coatings with excellent metallurgical bonding between layers on Q235 steel substrates by designing an appropriate interlayer structure and employing the high-speed laser-directed energy deposition (LDED). Through comprehensive evaluation of the composite coating's performance and the numerical simulations of heat transfer within the molten pool, we elucidated the impact of process parameter levels on the microstructure and phase transformation characteristics of the NiTi alloy coating (NTC). The phase composition and phase interface characteristics of the NTC surface and bonding interface were analyzed using an electron probe microanalyzer and transmission electron microscopy, while dynamic thermomechanical analysis was employed to evaluate the damping performance of the NTC. The results indicate that an optimal parameter combination area still exists within the NTC-LDED process parameter window, even with equal laser energy density. Insufficient parameter levels can lead to an increase of micro-defects within the NTC, consequently causing a deterioration in both the cohesion and deformation resistance of the coating. Excessively high parameter levels can lead to significant element loss and residual stress, which in turn contributes to an increase in microcracks within the coating. A considerable quantity of reaction product mixture phases was formed at the interface between NTC and NAB, tending to align coherently with the NAB phase interface. The NTC, prepared with optimal process parameters, exhibits exceptional damping performance with a damping ratio of 0.498 at internal friction equilibrium, rendering it highly promising for applications in surface erosion protection for fluid machinery.

Precipitation behavior and strengthening mechanism in a Cu-3.5Ti-0.1 Tm alloy

The study investigates the complex relationship between precipitation patterns, microstructural evolution, and mechanical properties in a Cu-3.5Ti-0.1 Tm alloy subjected to isothermal ageing. The results reveal that ageing at 450 °C leads to the formation of nanoscale β′-Cu4Ti phase particles within the grains and fibrous β-Cu4Ti precipitates along the grain boundaries. The precipitation microstructure of this aged alloy is predominantly characterised by tetragonal β′-Cu4Ti precipitates. During spinodal decomposition, Ti atoms segregate in rod-like Ti-rich Cu phases, facilitating their conversion into β′-Cu4Ti phase. The β′-Cu4Ti precipitates remain fully coherent with the Cu matrix, exhibiting a crystallographic orientation relationship of (001)Cu//(001)β′ and [100]Cu//[130]β′. As the precipitate radius exceeds approximately 11 nm, the elastic strain energy surpasses the energy at the precipitate/matrix interface. This leads to a shape transition from spherical to cuboidal for the β′-Cu4Ti precipitates. Moreover, the Ti solute atoms contribute significantly to the alloy's strength through solid solution hardening, with the dissolution of 1 at.% Ti solute increases the yield strength by 46.2 MPa. However, as ageing progresses from 1 to 20 h, the effect of solid solution strengthening decreases, while precipitation strengthening becomes more dominant, mainly due to the Orowan bypass mechanism. After 20 h of ageing, precipitation strengthening significantly increases the yield strength by about 436 MPa, exceeding the contributions from solid solution strengthening (78 MPa) and grain-boundary strengthening (14 MPa).

Carbon effect on tensile and wear behaviors for a dual-phase Fe61.5Cr17.5Ni13Al8 alloy

High entropy alloys (HEAs) series were produced by doping carbon into Fe61.5 Cr17.5Ni13-xAl8Cx (x = 0, 0.25, 0.5, and 1.5 at.%) by a vacuum arc melting. The carbon doping effect on the phase composition, mechanical properties, and wear behavior was studied. Fe61.5 Cr17.5Ni13Al8 alloy microstructure was a heterogeneous structure comprising FCC, BCC, and B2 phases. By introducing carbon into Fe61.5 Cr17.5Ni13-xAl8Cx (x = 0, 0.25, 0.5, and 1.5 at.%), the BCC phase fraction increased with decreasing FCC phase during annealing, accompanied by the formation of M23C6-like carbides at temperatures of 800 °C and 900 °C. The carbon-doped HEAs exhibited enhanced mechanical properties compared to the carbon-free HEAs, including higher tensile strength (1580 MPa), notable ductility (∼20 %), reduced friction coefficient (0.50), and improved wear resistance. Among the carbon-doped HEAs, the HEA with x = 0.5 at.% and annealed at 800 °C demonstrated exceptional wear resistance due to the compensations of attaining a balance between strength and elasticity.

Dislocation structures and residual stresses in duplex stainless steel fabricated by laser powder bed fusion with 430 and 316L powders

The duplex stainless steel is fabricated using laser powder bed fusion (LPBF), with raw materials prepared by mechanically mixing 430 and 316 L powders in a 1:1 mass ratio. The as-built alloys exhibit good overall mechanical properties, and theoretical strength calculations are performed based on the flow strength model. Uniquely, the distribution of dislocations, residual stresses, and strain accommodation mechanisms are investigated using electron backscattered diffraction and transmission electron microscopy. The results show that the microstructure of the as-built alloys is predominantly ferritic phase, with an austenitic phase content of approximately 4 %. The ultimate tensile strength is 938 ± 4 MPa and the elongation is 19 ± 0.58 %. The as-built alloys possess high dislocation densities, with the dislocation density in the ferritic phases being higher than in the austenitic phases. In particular, austenitic phases present barely any local misorientation and minimal rotations within grains, stacking faults are introduced to accommodate the solidification strains. However, ferritic phases exhibit a high dislocations density, with dislocations present on the (101), (011‾) and (211) planes, accommodating solidification strains and cooling stresses through elastoplastic deformation, and building up geometrically necessary dislocations.

Laser weldability and interface microstructure of CoCrNi-based medium-entropy alloy to Inconel 718 superalloy

Laser weldability and interface microstructure of CoCrNi-based medium-entropy alloy to Inconel 718 superalloy

Effect of Cr on the microstructure and corrosion behavior of nickel-based alloys in hydrochloric acid

Nickel-base alloy is a type of metal material with excellent properties and is widely used in many fields. However, in the harsh environment of the acid solution, corrosion causes the reduction of the service life of the alloys, thereby limiting the alloys' use and development. In this paper, the effect of Chromium (Cr) content on the microstructure and corrosion behavior of nickel-based alloys in hydrochloric acid (HCl) was studied by scanning electron microscopy (SEM), energy dispersive spectrum (EDS), electron backscatter diffraction (EBSD) and electrochemical workstation. Meanwhile, X-ray photoelectron spectroscopy (XPS) was used to investigate the composition and properties of the surface passive films. For the Cr20 and Cr30 alloys with a single face-centered cubic (FCC) structure, the Cr2O3 content in the passive films increased with the Cr content, effectively improving the corrosion resistance. As the Cr content continued to increase, the second phases having a body-centered cubic (BCC) lattice were precipitated both in the Cr40 and Cr50 samples, inducing microgalvanic corrosion, thus deteriorating the corrosion resistance. XPS results showed that, in the Cr30 alloy, the relative content of Cr2O3 and the bound water were the highest, indicating that its passive film had the best corrosion resistance. For the passive film, the pitting resistance was related to Cr content, appropriate Cr content improved the corrosion resistance.

Effect of annealing temperature on the microstructure and properties of TiZr2Ta alloy

The microstructure, mechanical properties, and corrosion resistance of annealed TiZr2Ta alloys were investigated. The results indicate that the corrosion resistance and wear resistance of the alloy have improved. This improvement is attributed to the annealing process, which eliminates residual stress and facilitates the formation and regeneration of surface oxide films. However, increasing the annealing temperature will lead to abnormal grain growth in the microstructure. The abnormal growth can be attributed to the energy released during the phase transition, which promotes the movement of grain boundaries. The high content of coarse grains in the alloy does not improve its mechanical properties or corrosion resistance.

Effects of scanning strategy and scanning speed on microstructures and mechanical properties of NiTi alloys by laser powder bed fusion

In this work, the influence of processing parameter including laser scanning strategy and scanning speed on grain morphology and crystalline orientation of NiTi alloys fabricated by laser powder bed fusion (L-PBF) was comprehensively investigated from the perspective of crystal growth. The results show that as the interlayer rotation angle increases from 0 to 90°, the grain morphology changes from the coarse columnar to columnar-and-equiaxed shapes, accompanied by the texture intensity first rising then reducing. Besides, increasing the scanning speed leads to a transition in grain morphology from columnar to equiaxed crystals, as well as a reduction in grain size and texture intensity. The recovery mechanism caused by different thermal histories under various scanning speeds was discussed, with a particular focus on dislocation density and its distribution. The results demonstrate that the dislocation density gradually increases with the increase of scanning speed, leaving behind more dislocations within the matrix. Furthermore, the effects of scanning speed and building direction on the compressive behavior were investigated through identifying the difference of microstructure in the NiTi alloys by L-PBF. This study highlights the relationship among processing, microstructure, and mechanical performance, paving the way for tailoring and designing microstructures and mechanical properties for the NiTi alloys by L-PBF.

Influence of Cu and Si on the microstructure and properties of CoCrFeNiCu1-xSix alloys

The effect of Cu and Si on the microstructure and properties of CoCrFeNiCu1-xSix alloys (x = 0, 0.2, 0.5, 0.8 and 1) was studied in this work. The results indicate that as the x value increased from 0 to 1, the phase compositions of CoCrFeNiCu1-xSix alloys evolved from FCC + Cu-rich phases to FCC + Cu-rich + NiSi-rich phases to FCC + BCC + NiSi-rich phases. Therefore, the decrease in Cu content led to the decreasing Cu-rich phase content, whereas Si addition not only favored the formation of intermetallic compounds, but also promoted the phase transition from FCC to BCC. Due to the competition between BCC phase suppressing corrosion and Cu-rich + NiSi-rich phases inducing galvanic corrosion, the corrosion resistance of CoCrFeNiCu1-xSix alloys improved with the increasing x value. The microstructure change also resulted in an improvement in hardness and wear resistance, and a deterioration in fracture toughness of CoCrFeNiCu1-xSix alloys. Moreover, the main wear mechanism evolved from adhesive wear and abrasive wear to slight abrasive wear. Comparison among five alloys indicates that Cu0.2Si0.8 alloy exhibited the excellent comprehensive properties, revealed by the corrosion current density of 4.81 × 10−8 A/cm2, the hardness value of 510.5 HV, the fracture toughness of 8.57 MPa·m1/2 and the wear rate of 0.88 mm3·N−1 · m−1.

The influence of high strain rates on mechanical properties and microstructure of CuCrZr alloy under strong current carrying condition

The extreme condition of high-speed metal deformation under intense current flow is commonly encountered in the realms of national defense, military, and industry. However, there has always been a lack of effective research method for the micro deformation mechanism of metal under this extreme condition. We have developed a high current and high strain rate tensile (HCHST) testing platform based on RC circuits, which is used to research the micro-deformation mechanisms of CuCrZr alloy under this extreme condition. The dynamic tensile tests of CuCrZr alloy at different high strain rates (1401s−1, 2957 s−1, 5503 s−1, 8012 s−1) under the high current density (6550 A/mm2) condition were conducted using the HCHST experimental platform. The mechanical properties and microstructure of CuCrZr alloy under the HCHST were analyzed by combining TEM and EBSD. The research results indicate that the microhardness of the alloy in the HCHST #1 environment (6550 A/mm2,1401s−1) is almost the same as the original state. This is attributed to the strong current promoting the movement of dislocations and reducing the accumulation of dislocations. Under condition like HCHST#1, the dislocation annihilation rate and dislocation formation rate of CuCrZr alloy almost reach equilibrium. At higher strain rates, the dislocation multiplication rate is much higher than the dislocation annihilation rate caused by strong current. This imbalance leads to dislocation entanglement and the formation of dislocation cells, resulting in an increase in the microhardness of the material. Additionally, EBSD was used to analyze the changes in grain size, average volume fraction of LAGBs, average KAM value, and texture of the samples, further verifying the dislocation evolution and microhardness changes of copper alloys under HCHST conditions. Our research results provide strong theoretical for the application of CuCrZr in the field of electrical thermal mechanical coupling.

Hot deformation behavior and microstructural evolution of titanium‐aluminum based alloy during hot compression

AbstractIn this paper, titanium‐aluminum based alloy was successfully prepared by introducing titanium powders using powder metallurgy. The experimental results indicated that the microstructures of alloys were composed of the new trititanium‐aluminium layers skeleton and the γ+α2 phases filler, which exhibited excellent compression properties. The compressive strength of the titanium‐aluminum based alloy (10 wt.% titanium) were 509.9 MPa, higher than monolithic Ti‐48Al‐2Cr‐2Nb alloy at 800 °C and 1×10−4 s−1. The deformation mechanism is mainly referred to the motion and rotation of γ+α2 areas and dynamic recrystallization. The γ+α2 areas were surrounded by complete new trititanium‐aluminium layers, which is beneficial to dislocation pile‐up, cross and tangle at grain boundaries, resulting in high strength. Besides, the dislocation pile of γ, α2 phase, and twins in γ phases, are the deformation mechanism in alloys.

Effect of tungsten carbide and titanium dioxide particles on the properties of aluminium alloy 5052 hybrid composites

AbstractAerospace and automotive industries, among others, utilize reinforced aluminium metal matrix composite materials extensively. Aluminium alloy 5052 matrix was reinforced with tungsten carbide and titanium dioxide particulate reinforcements by varying their weight fractions, to fabricate the hybrid composites. The melt‐stir casting route was used to process the materials, and their characteristics were determined by measuring Vickers microhardness, tensile strength and peak elongation. The cost‐effectiveness and productivity of the melt‐stir casting route led to its selection. Investigations were carried out to assess how reinforcement particles were mixed into the aluminium alloy matrix using scanning electron microscopy and energy‐dispersive x‐ray analysis. The microstructure of aluminium alloy 5052 showed a distinct homogenous structural integrity. Adding tungsten carbide and titanium dioxide particles to aluminium alloy 5052 led to a 6.57 % rise in the Vickers microhardness value. The tensile strength of the hybrid composites made of aluminium, tungsten carbide, and titanium dioxide increased by as much as 8.7 %. The findings demonstrated that all of the hybrid composites failed due to particle fracture and ductile fracture in the case of the as‐cast aluminium alloy 5052.