Grain Size Of Alloy Research Articles

Three-dimensional computational characterization of grain size and texture effects in magnesium alloys

This work systematically investigates the microstructure-property relationship in Mg alloys. Emphasis is placed on understanding, through high resolution crystal plasticity modeling, how grain size and texture collectively impact material strengthening and hardening, net plastic anisotropy, and tension-compression asymmetry. To achieve this, 528 fully three-dimensional finite element calculations are performed, which comprise eleven textures, four grain sizes, six loading orientations, and two uniaxial loading states (tension and compression). The grain size effect follows Hall-Petch relation that depends on both, loading orientation and initial texture. The reduction in extension twinning with grain size refinement is influenced by texture as well. Below a threshold textural strength, grain size refinement leads to an appreciable reduction in the net plastic anisotropy at yield, quantified using Hill anisotropy, and reduced tension-compression asymmetry. Using a micromechanical basis, the effect of grain size and texture on material ductility is predicted to be non-monotonic. The computational predictions serve as synthetic data sets for experimental validation and reduced-order modeling.

Revealing the effect of Si content on the microstructure and properties of Al–Si alloy by experiments and phase-field simulation

The grain size of aluminum alloy is closely related to solute content and solidification conditions. This study investigated the influence of Si content on the solidification microstructure and properties of the Al–Si binary alloy by experiments and phase field simulation. The experimental results indicated that the microstructure of Al–Si alloy changes from coarse columnar grains to uniformly distributed equiaxed grains as Si content increases from 0 to 7 wt%, and the average grain size of Al–2Si is the smallest (2.2 mm). Meanwhile, the tensile strength of Al–Si alloys increases from 56.9 MPa to 111 MPa with increasing Si content, whereas the ductility decreases from 30% to 2.5%. Moreover, high casting temperature will produce coarse columnar crystals, low casting temperature forms equiaxed crystals, the optimal casting temperature in this study is 30 °C above the liquidus. Phase field simulations reveal that the evolution of Al–Si microstructures is governed by two dimensionless parameters: the initial temperature (T0), related to casting temperature and solidification interval, and the latent heat (K1), connected to latent heat, specific heat, and solidification interval. For a certain alloy composition (Al–2Si), the grain size exhibits a non-monotonic trend, decreasing initially and then increasing as T0 increases, with an optimal T0 value of 1.42. When the Si content varies between 2 and 7 wt%, the average grain sizes decrease as K1 increases, with the maximum K1 value observed at 1.38 for Al–2Si.

The Effect of Heat Treatment on Phase Structure and Mechanical and Corrosion Resistance Properties of High Tungsten Ni-W Alloy Coating

The present study investigated the surface morphology, phase composition, mechanical properties, and corrosion resistance of Ni-W alloy coatings prepared under current densities of 1–5 A/dm², after undergoing heat treatment at 400 °C, 600 °C, and 900 °C. The grain size of the as-plated Ni-W alloy coating was below 10 nm. After heat treatment at different temperatures, the grain size increased, reaching a maximum value of around 30 nm at 900 °C. Heat treatment crystallized and altered the structure of the coating. Different heat treatment temperatures yielded different precipitates, including Ni4W, Ni6W6C, and WC. The highest coating hardness (820–940 Hv) was achieved at 400 °C, while the best corrosion resistance was achieved at 600 °C. The precipitation hardening phase can be obtained by proper heat treatment temperature, yielding the desired properties of the composite coating.

Exploring the mechanical, metallurgical, and fracture characteristics of hybrid-reinforced magnesium metal matrix composite synthesized via friction stir processing route

Low-cost hybrid-reinforced magnesium metal matrix composite (HMMC) materials present a revolutionary category of materials achieved by combining two or more distinct reinforcing elements within the magnesium (Mg) matrix. The main focus of this research is to fabricate Mg-based HMMCs with exceptional mechanical and other characteristics by utilizing Mg substrate AZ61A as the base material. To achieve this, nano-titanium carbide (TiC), nano-silicon carbide (SiC), and fly ash (FA) were selected as hybrid reinforcements, and the friction stir processing technique was employed for their incorporation. The microstructural, thermal, mechanical, wear, and fracture properties of synthesized HMMCs were carefully examined using a conventional testing approach. The findings demonstrate that the grain size of the base AZ61A alloy was measured at 32 µm, whereas the AZ61A/FA/TiC/SiC composite exhibited a remarkable reduction to 3.5 µm. Notably, this reduction in grain size leads to simultaneous enhancement in mechanical properties. The microhardness, ultimate tensile strength, and ultimate compressive strength of the developed HMMC showed an impressive increase, measuring 2.09 times, 2.75 times, and 2.10 times higher, respectively, compared to their initial values of the base material. Moreover, a significant enhancement in wear resistance was also observed, attributed to the increased hardness and homogenous hybrid reinforcement dispersion into the HMMCs. In addition, it was evident that the synergistic combination of different reinforcement particulates in Mg-based alloy improves overall fracture resistance and catastrophic failure and mitigates crack propagation.

Experimental investigation on wear resistance and corrosion behavior of nickel-aluminum bronze alloy fabricated by wire-arc additive manufacturing

This paper discusses the differences in the microstructure, mechanical properties, wear resistance, and corrosion behavior of nickel-aluminum bronze (NAB) alloys fabricated via wire arc additive manufacturing (WAAM) versus casting. The grain size of the WAAM-NAB alloy is smaller than that of the as-cast NAB alloys; furthermore, the precipitation of the large size κⅠ phase is completely suppressed while the remaining precipitated κ phases are limited and reduced in size. Compared with the cast alloy, the WAAM-NAB alloy indicates a higher bending and tensile strength by 46% and 18%, respectively. The coefficient of friction of WAAM-NAB alloy is 56% lower than cast alloys. Additionally, the WAAM-NAB alloy shows greater corrosion resistance against seawater, in that it only exhibited residual β phase corrosion, whereas the cast alloy sustained severe selective-phase corrosion.

Gradient microstructure and strength-ductility synergy improvement of 2319 aluminum alloys by hybrid additive manufacturing

Wire-arc additive manufacturing (WAAM) technology has been considered as a suitable method for manufacturing large components of aluminum alloys due to its high deposition rate and material utilization. However, the coarse grain size, high porosity and poor mechanical properties of as-deposited aluminum alloys have limited their further development. In this study, a novel hybrid additive manufacturing (HAM) technology combining WAAM and friction stir processing (FSP) has been developed, and a gradient microstructure 2319 aluminum alloy with ultrafine grains-equiaxed grains-columnar grains was successfully fabricated. The microstructure evolution and mechanical properties also have been investigated in this study. The grain size distribution, texture analysis, and the percentage of recrystallized grains were characterized by electron backscatter diffraction (EBSD). The experimental results demonstrated that the hybrid additive manufacturing can achieve a substantial grain refinement (87.09%) and increase the dynamic recrystallization content to 62% due to alternating mechanical and thermal effects. Meanwhile, compared with WAAM specimens, the hybrid-manufactured 2319 aluminum alloy has improved yield strength (YS) by 32.22%, ultimate tensile strength (UTS) by 8.75%, and elongation (EL) by 20%. The dominant mechanism of the significant strength-ductility synergy improvement also has been revealed.

Microstructure and Properties of Mg-Zn-Ca Alloy by Using Different Types of Cladding ECAP

A self-made 120° die was used for ECAP, and the effect of using different types of metal cladding and different temperatures for ECAP on the microstructure and mechanical properties of Mg-5Zn-0.6Ca alloy was analyzed. Microstructure observation and tensile testing were also carried out. The results show that, after ECAP, the grain size of the magnesium alloy was greatly refined, and the mechanical properties were significantly improved. Regarding the degree of grain refinement and the improvement of mechanical properties, 6061 aluminum alloy cladding is better than the pure copper cladding.

Diffusion behavior of Ta and Re in tungsten alloy with different addition methods

The addition of Ta or Re alone can improve the performance of tungsten alloys, but the combined addition of Ta and Re results in complex diffusion behavior and the formation of new phases. In this work, W-Ta-Re-Ni-Fe alloys with different Re contents were prepared by two methods (direct mixed powder sintering and pre-alloyed powder sintering), the compositions and structures of the precipitated phase through two preparation methods were analyzed, and the diffusion paths of Ta and Re were summarized. The addition of Re contributed to refining the grain size of tungsten alloys, but excessive Re addition led to the formation of hexagonal and tetragonal solid solution mesophases. Mechanical alloying not only strengthened the W particles substantially but also inhibited the growth of mesophases. In-situ Ni3Ta coherent nano-reinforced phase was generated by the diffusion reaction of Ta and Ni, which substantially increased the strength of the matrix phase. These findings suggest that the composite addition of Ta and Re is expected to further improve the toughness of tungsten alloys by adjusting the addition amounts of Ta and Re and improving the powder pretreatment.

Gaussian and circular oscillating laser directed energy deposition of WC/NiCu composites

In the realm of laser directed energy deposition (L-DED), the standard procedure typically using a Gaussian laser as the primary energy source. However, this well-established technique also has limitations as it generates considerable temperature gradients and residual stresses throughout the manufacturing process, resulting in notable deformation and cracking. To overcome these limitations, this study advocates for the replacement of the Gaussian laser with a circular oscillating laser. NiCu alloys and 16 wt% WC/NiCu composites were manufactured using the Gaussian laser and the circular oscillating laser deposition equipment. The results of this study reveal that the circular oscillating laser methodology exerts a pronounced agitation effect on the melt pool, thus hindering the formation of columnar dendrites and promoting the emergence of more nucleation sites for the growth of equiaxed dendrites. This method effectively refines the grains by reducing the temperature gradient of the melt pool and increasing the cooling rate. The average grain size of NiCu alloy manufactured using the circular oscillating laser is reduced by 19.5% compared to that manufactured using the Gaussian laser. The high temperature generated by laser and melt pool caused partial decomposition of WC into W and C, leading to the formation of W2C hard phases between the dendrites. Additionally, the unmelted WC particles were uniformly dispersed throughout the composites, which hindered the growth of columnar dendrites and refined the grains. Compared to the composites manufactured using the Gaussian laser, the composites manufactured using the circular oscillating laser exhibit an average microhardness increase of 15% and 11.1%, and a 76.5% and 22.2% decrease in wear rate, respectively. Composites containing 16 wt% WC manufactured using the Gaussian laser exhibit the best corrosion resistance.

Femtosecond Laser Preparation of Terracotta Warrior-like Pit Superhydrophobic Structure on Magnesium Alloy with Mechanical Durability and Corrosion Resistance.

Magnesium alloys are among the most promising materials for medical implants, and by preparing a superhydrophobic surface, the rate of corrosion can be effectively slowed down and durability be improved. However, the anticorrosion surfaces are inevitable to be damaged for the conventional micro-nanostructured superhydrophobic magnesium alloys, which highly limits their application prospects. This work proposes the development of a Terracotta Warrior pit superhydrophobic structure (TWPSS), consisting of a wall structure with a Terracotta Warrior-like pit and a lotus-like surface papillae structure within the wall. For the first time, top-down laser ablation of the pits to prepare the lotus-like surface papilla structure is used in conjunction with a bottom-up laser-guided melt stacking of the raised wall structure to achieve rapid fabrication of a TWPSS on a magnesium alloy surface. The Cassie-Baxter-based design of the wall structure spacing effectively protects the internal lotus-like surface papillae from damage and the disappearance of low surface energy material, and the results show that the superhydrophobic surfaces of magnesium alloys have excellent mechanical durability and repairability. In addition, it was found that the recast layer and laser melting stacked layers produced on the surface of the alloy during femtosecond laser processing refined the grain size of the magnesium alloy and effectively suppressed the corrosion rate. The combination of the superhydrophobic gas layer and the resulting grain refinement slowed down the corrosion of the magnesium alloy. Thus, the rapid preparation of TWPSS structures with mechanical durability and corrosion resistance by femtosecond lasers expands the clinical applications of superhydrophobic surface magnesium alloys in medical devices.

Reduced lattice thermal conductivity through tailoring of the crystallization behavior of NbCoSn by V addition

Nanostructuring is a key approach for reducing lattice thermal conductivity. Amorphous precursors can be used to obtain complex nanostructures, as their crystallization behavior can be controlled by varying their composition, temperature, and annealing time. Herein, we investigated the effects of V alloying on the crystallization behavior and resulting lattice thermal conductivity of amorphous NbCoSn alloys. After heat treatment at 783 K for 2 h, the V-containing alloy showed a significantly finer grain size (100 ± 30 nm) than the alloy without V (870 ± 360 nm) owing to the different crystallization kinetics. We revealed that Sn-rich nanoprecipitates with a diameter of 10 nm acted as heterogeneous nucleation sites for crystallization, resulting in a finer grain size in the V-containing alloy. As a result, the V-containing alloy exhibited a lower lattice thermal conductivity (2.6 ± 0.2 W m−1 K−1) than the alloy without V (3.3 ± 0.2 W m−1 K−1) at room temperature owing to increased phonon scattering at the grain boundary, point defects, and nanoprecipitates.

Low-Cycle Fatigue Behavior and Fracture Characteristics of Low-Cost Ti-2Fe-0.1B Alloy

In recent decades, the effect of Fe element addition on titanium alloy has been investigated extensively due to the development of low-cost titanium alloys, as well as B microalloying, which could decrease the grain size of titanium alloys during the casting process. As a key structural material, the study of the fatigue behavior of titanium alloys is crucial and always attractive for scientists. Hence, in this paper, the low cycle fatigue (LCF) behavior and fracture characteristics of a low-cost Ti-2Fe-0.1B alloy with a lamellar structure were investigated systematically, five different strain amplitudes (Δεt/2) in the range from 0.6% to 1.4% were selected to control the LCF process. It was found that the Ti-2Fe-0.1B alloy exhibits continuous cyclic softening behavior in the cycle as a whole at Δεt/2 ≤ 1.2%, while at Δεt/2 = 1.4%, it exhibits slight cyclic hardening at the initial stage of the cycle, then shows cyclic softening. Compared with pure titanium and other typical titanium alloys, the Ti-2Fe-0.1B alloy indicated maximum fatigue life under the same strain amplitude, it can be attributed to the fine grain size result from the effect of Fe element and trace B, which could hinder the dislocation movement and crack propagation.

A combined experimental and crystal plasticity study of grain size effects in magnesium alloys

This work presents a method to incorporate the micro Hall-Petch equation into the crystal plasticity finite element (CPFE) framework accounting for the microstructural features to understand the coupling between grain size, texture, and loading direction in magnesium alloys. The effect of grain size and texture is accounted for by modifying the slip resistances of individual basal and prismatic systems based on the micro Hall-Petch equation. The modification based on the micro Hall-Petch equation endows every slip system at each microstructural point with a slip system-level grain size and maximum compatibility factor, which are in turn used to modify the slip resistance. While the slip-system level grain size is a measure of the grain size, the maximum compatibility factor encodes the effect of the grain boundary on the slip system resistance modification and is computed based on the Luster-Morris factor. The model is calibrated using experimental stress-strain curves of Mg-4Al samples with three different grain sizes from which the Hall-Petch coefficients are extracted and compared with Hall-Petch coefficients predicted using original parameters from previous work. The predictability of the model is then evaluated for a Mg-4Al sample with different texture and three grain sizes subjected to loading in different directions. The calibrated parameters are then used for some parametric studies to investigate the variation of Hall-Petch slope for different degrees of simulated spread in basal texture, variation of Hall-Petch slope with loading direction relative to basal poles for a microstructure with strong basal texture, and variation of yield strength with change in grain morphology. The proposed approach to incorporate the micro Hall-Petch equation into the CPFE framework provides a foundation to quantitatively model more complicated scenarios of coupling between grain size, texture and loading direction in the plasticity of Mg alloys.

Microstructure Refinement and Work-Hardening Behaviors of NiAl Alloy Prepared by Combustion Synthesis and Hot Pressing Technique

Most methods used to synthesize and prepare NiAl intermetallics and their alloys have the disadvantages of complexity and high cost. In this paper, the NiAl alloy was prepared by a Combustion Synthesis and Hot Pressing (CSHP) technique under rapid solidification. The grain size of the NiAl alloy is significantly refined to 60–80 μm, which reduces the stress concentration during deformation and improves the fracture strength and fracture hardness. Moreover, the large internal stress and greater amount of dislocations in the as-cast microstructure are produced by their formation under pressure due to the fast cooling rate in the solidification process. The high dislocation density strengthens the NiAl alloy, giving it higher strength, hardness, and work-hardening ability. The high compression properties are also present in the NiAl intermetallics at room temperature, in which the fracture strength is around 1005 MPa and the fracture strain reaches 21.6%. The compressive fracture strength at room temperature is higher than that of the pure NiAl alloy prepared by the Hot-Pressing-Aided Exothermic Synthesis (HPES, about 632 MPa), while it is slightly lower than that of pure NiAl alloy treated by HPES and Hot Isostatic Pressing (HIP, 1050 MPa). The fracture strain is significantly higher than that of the NiAl alloy prepared by other methods. This study can provide guidance for the successful preparation of the NiAl alloy with high strength and toughness.

Accelerated development of Ti-6Al-4V microbial corrosion triggered by electroactive sulfate-reducing Desulfovibrio ferrophilus biofilm in enriched artificial seawater containing soluble electron shuttle

In this work, microbial corrosion behavior of Ti-6Al-4V (TC4) alloy caused by electroactive Desulfovibrio ferrophilus biofilm in enriched artificial seawater containing soluble electron shuttle was investigated. The addition of riboflavin-shuttle did not significantly change the planktonic and sessile cell counts but accelerated the microbiologically influenced corrosion of TC4 alloy. The Hilbert-Huang transform revealed the evolution of corrosion pits and the maximum pit depth enhanced with the increase of electron shuttle concentration. Electrochemical measurements proved that riboflavin-shuttle decreased the shuttled electron barrier and increased the anodic dissolution rate. Phase, organization and grain size of alloy were influenced by the MIC.

Maximizing the scattering of multiwavelength phonons in novel biphasic high-entropy ZrCoSb-based half-Heusler alloys

The thermoelectric (TE) performance of p-type ZrCoSb-based half-Heusler (HH) alloys has been improved tremendously in recent years; however, it remains challenging to find suitable n-type ZrCoSb-based HH alloys due to their high lattice thermal conductivity (κL). In this work, n-type Zr1−xTaxCo1−xNixSb HH alloys were firstly designed by multisite alloying. The evolution of the Raman peak proved that alloy scattering, phonon softening, anharmonicity, entropy-driven disorder, and precipitates had a combined effect on decreasing κL by 46.7% compared to that of pristine ZrCoSb. Subsequently, Hf0.75Zr0.25NiSn0.99Sb0.01 was introduced into Zr0.88Ta0.12Co0.88Ni0.12Sb to further suppress κL. Remarkably, the grain size of the biphasic HH alloys was refined by at least one order of magnitude. A biphasic high-entropy HH alloy with y = 0.2 exhibited the minimum κL of ∼2.44 W/(m·K) at 923 K, reducing by 67.7% compared to that of ZrCoSb. Consequently, (Zr0.88Ta0.12Co0.88Ni0.12Sb)0.9(Hf0.75Zr0.25NiSn0.99Sb0.01)0.1 exhibited the highest TE figure of merit (∼0.38) at 923 K. The cooperation between the entropy and biphasic microstructure resulted in multiscale defects, refined grains, and biphasic interfaces, which maximized the scattering of the multiwavelength phonons in HH alloys. This work provides a new strategy for further reducing the grain size and κL of medium- and high-entropy HH alloys.

Investigation of the Microstructure and Wear Properties of Conventional Laser Cladding and Ultra-High-Speed Laser Cladding Alloy Coatings for Wheel Materials

In this paper, Fe-based and Co-based alloy powders were chosen to perform laser cladding on wheel materials through conventional laser cladding (CLC) and ultra-high-speed laser cladding (UHSLC) processes, respectively. The microstructures, element distribution, phase composition and hardness of the Fe-based alloy and Co-based alloy coating layers using the CLC and UHSLC processes were compared and analysed. The results show that the CLC and UHSLC alloy coatings were dense and free of defects such as pores and cracks. Compared with the CLC alloy coating, the grain size of the UHSLC alloy coating was smaller, the coating composition was close to the powder design composition, and the distribution of Cr within and between the grains was more uniform. The Fe-based coating was mainly composed of (Fe, Ni) and Cr7C3, and the Co-based coating was mainly composed of γ-Co and Cr23C6. It was found that the cooling rate of the CLC alloy coating was smaller than that of the USHLC, and the hardness of the CLC alloy coating was less than that of the USHLC. The average hardness of the UHSLC Fe-based and Co-based alloy coatings was 709 HV and 525 HV, respectively. The average hardness of the CLC Fe-based and Co-based alloy coatings was 615 HV and 493 HV, respectively. The rolling friction and wear tests were carried out with the CLC-treated and UHSLC-treated wheel specimens on the GPM-30 rolling contact fatigue testing machine. The results showed that the wear rate of the UHSLC alloy coating on the wheel specimens was significantly lower than that of the CLC alloy coating on the wheel specimens. The wear rates of the UHSLC Fe-based and Co-based alloy coatings on the wheel specimens were reduced by 40.7% and 73.8%, respectively. It was demonstrated that the wear resistance of the USHLC alloy coatings was better than those of the CLC alloy coatings. The CLC alloy coating exhibited more severe fatigue damage with small cracks. Furthermore, the damage of the UHSLC alloy coating was relatively minor, with slight spalling. The Co-based alloy coating exhibited superior wear properties with the same laser cladding process.

The Effect of Boron Addition on the Structure and Mechanical Properties of Cu–Al–Ni–B Alloys with a Thermoelastic Martensitic Transformation

For the first time, data on the peculiarities of the structure of the Cu–Al–Ni–(B) alloys differing in the contents of alloying elements, namely, containing 10–14 wt % aluminum, 3, 4, 4.5 wt % nickel, and 0.02–0.3 wt % boron were obtained using optical, scanning, and transmission microscopy and X-ray diffraction analysis along with measurements of tensile mechanical properties. The effect of boron on the grain size, structure, phase composition, and mechanical properties of the shape-memory alloys has been studied. The localization of aluminum boride precipitates in the structure has been studied, and the effect of grain growthretardation in (α + β) and β Cu–Al–Ni–B alloys in both cast and heat-treated states has been found.

Low-temperature diffusion bonding of Ti6Al4V alloy via nanocrystallization and hydrogenation surface treatment

Hydrogenation and nanocrystallization of Ti6Al4V alloy were achieved by electrolytic hydrogenation and SMAT processing. The hydride δ phase appeared when the hydrogenation time reached 4 h. The grain size of Ti6Al4V alloy after surface nanocrystallization reached below 35 nm when the SMAT processing time was 2 h. Surface morphology and roughness were characterized by AFM. The diffusion bonding between Ti6Al4V alloys at low temperature was achieved under different parameters. It is demonstrated that the porosity at the interface decreased correspondingly when the hydrogenation time or nanocrystallization time was extended. The porosity of the joint reached 0 when the hydrogenation time was 24 h or the nanocrystallization time was 4 h. Then hydrogenation and nanocrystallization treatments were combined. It is found that there are more bonding defects in both hydrogenation-nanocrystallization and nanocrystallization-hydrogenation joints than in joints with single hydrogenation or nanocrystallization treatment. It can be concluded that the porosity of the joints with nanocrystallization first is lower than that with hydrogenation first.

Effects of titanium addition on austenite grain size and mechanical properties of high manganese steel

Manganese steels have been widely used in industries due to their good wear resistance, high work hardening ability, and high toughness and ductility. This research investigated the effect of modification, i.e., FeTi and Mischmetal, on the grain size and mechanical properties of the high manganese steel (13–15 wt.%). The alloys are modified at different temperatures of 1500, 1550, and 1600 o. The modified alloys were heat-treated after solidification by a two-step process. The grain size, chemical composition, and phase formation of the heat-treated steel were characterized by Optical Microscopy, X-ray Diffractometry, and Energy-Dispersive X-ray Spectroscopy. The mechanical properties of the steel, such as Brinell hardness, tensile strength, and toughness, were measured. As a result, the grain size of the heat-treated alloys is smaller compared to that of un-modified alloys and decreases with the increase in modification amount. The addition of Ti reduced C in the austenite phase by forming very stable carbides, TiC. Maximum tensile strength of 780 MPa was achieved with the addition of 0.1 wt.% Ti, while maximum fracture toughness was 140 J/cm2 at 0.05 wt.% Ti.