Dispersion Of Second Phase Particles Research Articles

Formation mechanism of AlNbTiVZr high entropy alloy/Ti multi-principal element alloy by laser direct energy deposition: Microstructure evaluation and mechanical properties

A novel refractory multi-principal element alloy with high strength and toughness matching characteristics was successfully prepared by mixing TA15 alloy with AlNbTiVZr high-entropy alloy. The effects of the composition ratio of the high-entropy alloy on the microstructure evolution and its influence on properties were investigated in this study. The tensile strength of the 70wt.% AlNbTiVZr HEA/Ti multi-principal element alloy is 1.18 times more than that of TA15 alloy, which has a value of 1068.0 ± 2.1MPa. The increase in strength is mainly due to the production of equiaxed fine grains and the development of a robust and resilient body-centered cubic (BCC) phase in the alloy following the introduction of the high-entropy alloy. The attainment of the acceptable tensile strain is the result of the combined influence of the BCC matrix phase and the dispersed second-phase particles. The exceptional mechanical capabilities of the 70wt.% AlNbTiVZr/Ti multi-principal element alloy undeniably enhance its potential for use as a structural component in aerospace load-bearing constructions.

Effect of Bi alloying and cold rolling on microstructure and mechanical properties of LA141 Mg[sbnd]Li alloy

LA141-xBi (x = 0, 1, 2, 3) alloys were prepared, and the effects of Bi alloying and cold rolling on the microstructure and mechanical properties were investigated. The results indicate that, with the addition of Bi, the grains were refined, and Mg3Bi2 phase is formed in the alloys. The as-cast LA141-2Bi possesses the tensile strength of 174 MPa, 21% higher than that of LA141 alloy. The cold rolled LA141-2Bi alloy exhibits a good balance between strength and plasticity, with a tensile strength of 237 MPa and an elongation of 30.5%. This improvement is primarily attributed to grain refinement, the dispersion of second-phase particles, high-density dislocations, and the presence of nano-twins.

Microstructure Features and Mechanical Properties of Modified Low-Activation Austenitic Steel in the Temperature Range of 20 to 750 °C

A new low-activation austenitic steel with a modified composition and high austenite stability is proposed. The features of its microstructure after solution treatment (ST) and cold rolling (CR) are studied. The mechanical properties and features of the fracture behavior of this steel under tensile tests in the temperature range of 20–750 °C are discussed. After ST, an austenitic structure with stacking faults and dispersed carbide particles of the MC and M23C6 types is observed in the steel. After CR, the grains are refined, and the average grain size decreases from 41.4 µm (after ST) to 33.9 µm. High-density microtwin packets form in the material, and the dislocation density increases relative to that after ST. As the test temperature increases from 20 to 750 °C, the yield strength of the steel decreases by approximately two times, from ≈300 to 150 MPa (for ST) and from ≈700 to 370 MPa (for CR). In the studied temperature range, the steel demonstrates up to 2.6 times higher values of elongation to failure, ≈40–80% (for ST) and ≈13–27% (for CR), compared to steels of similar compositions and lower manganese content. Mechanical twinning contributes to the high steel ductility up to 300 °C. Signs of discontinuous flow in the tensile curves after ST in the temperature range of 500–600 °C and a decrease in the elongation to failure in the close temperature range indicate dynamic strain aging (DSA). Steel fracture after tension at all test temperatures mainly occurs via a ductile dimple transcrystalline mechanism with elements of ductile intercrystalline fracture. It is shown that cracks nucleate on clusters of dispersed second-phase particles. The mechanisms of plastic deformation, fracture, and strengthening of the proposed modified low-activation austenitic steel are discussed.

Third-generation biodegradable bone implants: A novel Mg-1Zn-0.5Sc alloy treated by laser shock peening to improve its characteristics

Magnesium (Mg) and its alloys are of much interest as promising third-generation bio-materials for bone implant applications; however, challenges remain for the alloy's mechanical integrity and bio-corrosion behaviour. Therefore, appropriate alloying elements and surface-modification techniques are required to overcome these limitations. Zinc and scandium were found to possess good biocompatibility and biodegradability, in addition to magnesium. This study aims to enhance the mechanical integrity and bio-corrosion resistance behaviour of a novel Mg-1wt% Zn-0.5wt% Sc cast alloy by laser shock peening surface treatment with multiple passes (LSP-2 pass and LSP-3 pass). The microstructural and texture evolution was investigated using various techniques, including field emission scanning electron microscopy with energy-dispersive spectroscopy (FESEM-EDS), optical microscopy (OM), X-ray diffraction (XRD) analysis, electron back-scattered diffraction analysis (EBSD), as well as the surface residual stress, wettability, microhardness, tensile strength, electrochemical polarization test, and biocompatibility were analysed on as-cast, LSP-2 pass and LSP-3 pass specimens. LSP induced beneficial compressive residual stress around the surface and sub-surface region of Mg-1Zn-0.5Sc alloy due to severe plastic deformation, which led to grain refinement through the twinning mechanism of the Mg alloy. Also, the dispersion of second-phase particles (β-ScZn) was observed while analysing the XRD profiles. Strain hardening, grain refinement, and precipitate strengthening have contributed to the structure and texture evolution, which enhanced the microhardness, tensile strength, ductility, and corrosion resistance of the Mg-1Zn-0.5Sc alloy. From in vitro studies, a low rate of corrosion in simulated body fluid and less cytotoxic behaviour were observed for the LSP-3 pass Mg-1Zn-0.5Sc alloy.

Synergetic effects of cryo-FSP on microstructural, mechanical and corrosion behavior of stir cast AA5083-2 wt% SiC nanocomposite

In recent past, a significant research attention has been given to the study of nanosize ceramic particles reinforced aluminium alloy composites due to its excellent mechanical and surface properties compared to unreinforced counterpart. Hence, the major aim of the present study is to investigate the effects of cryocooling friction stir processing (cryo-FSP) on microstructural evolution, and its effects on mechanical properties & corrosion behavior of a stir-cast 2 wt% nanosize SiC (n-SiC) particles reinforced AA5083 nanocomposite in comparison to the room temperature (RT) FSPed and as cast counterparts. The cryo-FSP was performed successfully using optimized process parameters of 1400 rpm and 40 mm/min traverse speed using a specially designed cryo-FSP setup extracting deformation heat efficiently by a flowing mixture of LN2 and methanol (−30 °C). Evolution of a finer equiaxed grain structure (∼2 μm) with a homogeneous distribution of n-SiC particles and precipitate phases is confirmed (through SEM-EBSD and STEM/TEM analysis) in the cryo-FSPed composite compared to RT-FSPed sample (∼4 μm). The cryo-FSPed sample exhibited a superior yield strength (i.e., YS = 230 ± 3 MPa) compared to the RT-FSPed sample (i.e., YS = 197 ± 4 MPa) with a reasonably good ductility for both (i.e., 14 %). The improved YS is attributed mainly to the grain boundary strengthening due to extra grain refinement induced by cryo-FSP and dispersion strengthening via second phase particles. Different strengthening mechanisms' analyses established a good correlation between the theoretical YS and experimentally obtained tensile YS. Fractography analysis corroborated well with the tensile properties of the corresponding samples. Compared to the interdendritic cast structure, both the FSPed samples exhibited a superior corrosion resistance due to an improved surface characteristic developed in the dynamically recrystallized matrix with uniform dispersion of second phase particles. However, due to more grain boundary active phenomenon and higher misorientation angles, a bit higher corrosion rate could be observed in the fine-grained cryo-FSPed sample compared to the RT-FSPed composite.

Consolidation of Zn-Hydroxyapatite and Zn-Bioactive Glass Composites Using High-Pressure Torsion

There has been a great interest in developing zinc-based composites for biological applications. Mixing bioactive particles and obtaining a well-dispersed structure is not straight forward though. The present study reports a novel processing route in which zinc particles are mixed with hydroxyapatite and bioactive glass particles and consolidated at room temperature using high-pressure torsion. The composites display good dispersion of second phase particles, enhanced strength and an increased corrosion rate in the Hank’s balanced salt solution. The incorporation of these particles can be used to tailor the corrosion rate of zinc. It is shown that the surface layer of the corrosion product in the zinc-bioactive particle composites is richer in calcium and phosphorous than the pure zinc counterpart.

Microstructure evolution and mechanical properties of the Mg–5Al–1Mn-0.5Zn-xCa alloys prepared by regular extrusion

High strength-ductility synergy Mg–5Al–1Mn-0.5Zn-xCa (x = 0.5, 1 and 2, in wt.%) alloys without rare earth elements were prepared by conventional extrusion at 360 °C with an extrusion ratio of 25:1. The microstructure evolution and mechanical properties of Mg–5Al–1Mn-0.5Zn-xCa alloys were investigated by OM, XRD, SEM, EBSD, TEM and tensile tests. The as-extruded alloys are almost fine equiaxed grains with dispersed particles (Al2Ca, Al8Mn5, Mg2Ca and nanoscale (Al, Mn)-rich precipitates). With the increase of Ca addition, the average grain size decreases, the fine particles increase and basal textures become stronger, which result that the strength of the extruded alloy increases gradually while the elongation decrease. As-extruded Mg–5Al–1Mn-0.5Zn–2Ca exhibits excellent comprehensive mechanical properties of the ultimate tensile stress (UTS) of 340 MPa and fracture elongation (FE) of 12.8% with fine grains (2.42 μm), strong basal texture, high density of precipitates and dislocations. The TEM results show that Ca and Zn are segregated at the grain boundaries and a large amount of dispersed second-phase particles existed in the Mg–5Al–1Mn-0.5Zn–2Ca alloy, which is beneficial to grain refinement. Besides, the activated nonbasal slips are beneficial to the ductility which result from the restriction of twinning in fine grains and high Schmid factor (SF) of nonbasal slips.

Study on Sc Microalloying and Strengthening Mechanism of Al-Mg Alloy

In this study, Al-Mg alloys were prepared by vacuum + argon-protected casting. The effects of Sc microalloying on the microstructure and mechanical properties of Al-Mg alloy were studied. The strengthening mechanism of Al-Mg alloy with Sc was discussed. The results show that the average grain size of as-cast Al-Mg alloy with Sc reaches 36.07 μm, which is 74.4% smaller than that of alloy 1 without refiner and 32.0% of alloy 2 with 0.15% Ti. The alloy with Sc has excellent comprehensive mechanical properties, with a tensile strength of 274 MPa and an elongation of 29.67%, and its tensile strength is 10.6% higher than alloy 1 and 7.9% higher than alloy 2. There exist two kinds of fine particles in as-cast Sc-containing Al-Mg alloy, nucleated particles Al3Sc, and dispersed second-phase particles Al3(Sc, Ti). The main strengthening mechanisms of the as-cast Al-Mg alloy with Sc reveal the solid solution strengthening of Mg and the fine-grain strengthening effect caused by Sc, accounting for 57.7% and 23.9% to strengthening contribution, respectively.

Synergistic effects of hybrid (HA+Ag) particles and friction stir processing in the design of a high-strength magnesium matrix bio-nano composite with an appropriate texture for biomedical applications

In this work, the effects of hybrid (HA + Ag) particles and triple-pass friction stir processing on the microstructure, texture, hardness, and tensile behavior of magnesium matrix bio-nano composite were investigated. The results showed that the mean grain size of samples was in the range of 1–5 μm owing to the occurrence of dynamic recrystallization and suppression of grain growth by second phase particles. All samples exhibited uniform dispersion of particles in the magnesium matrix caused by triple-pass FSP. However, some agglomerations were visible in the microstructure of AZ91/nHA nanocomposite. The average grain size of the AZ91/nHA/smAg sample (1.4 μm) was smaller than that of the AZ91/nHA/mAg sample (2.1 μm), which was attributed to the formation of higher content of MgxAgy precipitates in the AZ91/nHA/smAg composite. By performing the FSP, the content of Mg17Al12 was significantly decreased due to the dissolution of beta into the alpha caused by the breakup effect of mechanical stirring and temperature increase of samples. The AZ91/nHA/smAg sample had the highest texture parameter for the {101‾1} orientation as the high corrosion resistance texture. This was due to the promoting the non-basal slip caused by the dissolution of smAg particles in the magnesium matrix. After the FSP, the microhardness distribution of AZ91, AZ91/nHA, AZ91/nHA/mAg, and AZ91/nHA/smAg samples tended to be uniform and the average hardness was improved owing to the fragmentation of beta particles, grain refinement, and homogeneous dispersion of second phase particles. Compared with the AZ91/nHA/mAg sample, an increase in ultimate tensile strength (291.7 MPa), and a decrease in total elongation (5.6%) and energy absorption (12.3 J/cm3) were observed in the AZ91/nHA/smAg sample due to the formation of a higher content of the silver-rich precipitates in the AZ91/nHA/smAg sample during cooling caused by the higher solubility of silver submicron particles. The fracture surfaces of all processed samples consisted of a large number of fine equiaxed dimples (ductile fracture) owing to the grain refinement and the presence of fine second phase particles.

Surface integrity evolution of Nb-Ti microalloyed steels along the gear manufacturing chain

The increasing demand for high performance gears requires in-depth investigations of alternative materials to those commonly used. In this respect, microalloyed steels may appear as an alternative with technical and economic potential. Microalloyed steels may exhibit a more refined grain structure than conventional steels, which is commonly induced by the precipitation of highly stable and dispersed second-phase particles. This investigation aimed at understanding how the steel grain structure obtained by the addition of niobium (Nb) and titanium (Ti) as microalloying elements correlates to the material surface integrity promoted by a conventional gear manufacturing chain. The results indicated that the addition of microalloying elements leads to a refined and homogeneous grain structure. The residual stress state also proved to be both more compressive and homogeneous and the roughness exhibited greater stability. Such characteristics place the microalloyed steels in a prominent position regarding their application in the gear manufacturing, indicating the possibility of fatigue lifetime improvement.

Prominent role of multi-scale microstructural heterogeneities on superplastic deformation of a high solid solution Al–7Mg alloy

Achieving high superplasticity in single-phase Al alloys remains a challenge, since the fine-grained structure required for superplastic deformation coarsens rapidly in the absence of dispersed second-phase particles during tensile deformation at elevated temperatures. This paper concentrates on the superplastic response of a high solid solution Al–7Mg alloy processed by equal-channel angular pressing (ECAP) under uniaxial tension. The ECAP-processed Al–7Mg alloy features multi-scale microstructural heterogeneities including a bimodal grain structure and Mg solute segregation along grain boundaries (GBs) of nano/ultrafine grains. To identify effects of multi-scale microstructural heterogeneities on superplastic deformation behavior of the high solid solution Al–7Mg alloy, microstructural evolutions are studied systematically by combing electron backscatter diffraction (EBSD), ASTAR-transmission electron microscopy (TEM) orientation imaging and atom probe tomography (APT). During deformation at the optimal tensile condition of 573 K and 1 × 10−3 s−1, the heterogeneous microstructure evolves to a stable uniform fine grain structure via continuous dynamic recrystallization (CDRX), and impressive superplasticity of ∼523% elongation is achieved. The high superplasticity is discussed in terms of the cooperated mechanism by dislocation slip accommodated by CDRX at the early tensile deformation stage and grain boundary sliding (GBS) at the late deformation stage. Our findings show that the evolution of microstructural heterogeneities in high solid solution Al–Mg alloys can be regulated, favoring for superplastic deformation, which offers an alternative strategy for developing low-cost Al alloys for enhanced mechanical properties.

In-situ microstructural control of A6082 alloy to modify second phase particles by melt conditioned direct chill (MC-DC) casting process – A novel approach

• High shear melt conditioning in the sump during direct chill casting of A6082 billet. • Novelty of maintaining 2–7 °C above alloy liquidus as the sump thermal condition. • In-situ control of solidification during casting by intensive melt shearing. • Precise tailoring of as-cast microstructure to modify second phase particles. • Potential for industries to eliminate homogenisation and use recycled Al alloys. Controlling the formation of noncompact second phase particles during direct chill (DC) casting of aluminium alloys with grain refiner addition remains challenging, as it results in energy intensive homogenisation and deformation problems. In this work, we employed a novel strategy in the DC casting of A6082 alloy to produce billets with a fine-scale dispersion of second phase particles. The strategy involves maintaining 2–7 °C above alloy liquidus as a thermal condition in the sump by in-situ melt conditioning (MC) using a rotor-stator high-shear device operated at a critical rotation speed. As a result, in-situ control of solidification behaviour is achieved to precisely tailor the as-cast microstructure. The billet grain refinement is attained by MC-DC casting without the deliberate addition of chemical grain refiners. The microstructure of the MC-DC cast billet at the critical rotation speed showed a fine-scale dendritic structure with refined secondary dendrite arm spacing (SDAS). The solidification front proceeded with a shallow sump and a corresponding shorter solidification time, higher cooling rate, higher temperature gradient, and smooth solidification rate profile. The ideal fine-scale dendrites with low SDAS divided the remaining eutectic liquid into fine-scale and isolated liquid pockets, resulting in fine-scale, compact morphology, and uniform distribution of second phase particles in the as-cast microstructure. The MC-DC casting process showed the ability to increase the cast house production rate by increasing the casting speed without bleeding the billet. The present approach could be beneficial for eliminating or reducing the homogenisation practice and may also introduce significant flexibility in using recycled Al alloys in the industry.

Austenite Grain Growth Behaviors of La-Microalloyed H13 Steel and Its Effect on Mechanical Properties

Controlling austenite grain size is an effective method to improve mechanical properties of alloy steels. This article shows that La addition can effectively restrain the growth of austenite grains in H13 steel and make the grain size distribution more uniform. When holding at 1050 °C from 10 to 180 minutes, the average austenite grain of La-microalloyed H13 steel increases by 35.7 pct, while that of La-free H13 steel increases by 66.7 pct. With the extension of austenitizing time, the decrease in the strength and the plasticity of tempered La-microalloyed H13 steel is considerably less than those of tempered La-free H13 steel. Austenitized at 1050 °C for 180 minutes, the tensile strength and the elongation to failure of the tempered La-microalloyed steel are 1895 MPa and 9.3 pct, respectively. The addition of La increases the amount of undissolved carbide V8C7 and refines the carbide, and La2O2S particles with high melting point are detected. Because of the combined effect of these fine dispersed second-phase particles, the pinning effect on grain boundary migration increases, and the grain growth is restrained. Some martensitic substructures transform from twin configuration to dislocation configuration because of La addition, and the lath bundles of martensite are refined. As a result, the strength and the toughness of the steel are improved.

Tailoring the mechanical properties of Mg–Zn magnesium alloy by calcium addition and hot extrusion process

Grain refinement and enhanced mechanical properties of Mg–2Zn-xCa alloys (with a wide range of calcium contents from 0 to 5 wt%) were studied in both as-cast and extruded conditions. It was revealed that Ca addition can effectively refine the grain size of the ingots based on the growth restriction factor (GRF) mechanism, where at high Ca additions, the dendritic microstructure was obtained. By increasing the amount of Ca, the binary Mg–Zn phase was replaced by the Ca2Mg6Zn3 phase and at high Ca contents, the Mg2Ca phase appeared in the microstructure. The tensile properties were enhanced at low Ca additions (up to 0.3 wt%) due to the grain refinement but they were deteriorated at higher Ca additions due to the formation of grain boundary second phases. Accordingly, the ultimate tensile strength (UTS) of 228 MPa and total elongation of 20% was obtained for the as-cast Mg–2Zn-0.3Ca (ZX20) alloy. During hot extrusion, significant grain refinement and the fracturing and dispersion of second phase particles were observed. The grain size refinement beyond ~1 wt% Ca was negligible and extrusion defects were observed at higher Ca contents, and hence, the best combination of mechanical properties was obtained for the Mg–2Zn–1Ca (ZX21) alloy with UTS of 283 MPa and elongation to failure of 29%. This alloy showed a desirable work-hardening behavior and the best combination of tensile properties, where the product of tensile strength and total elongation reached as high as ~8000 MPa%. Finally, the yield stress of the alloys was correlated to the average grain size via the classical Hall-Petch plot with a slope of 228.5 MPa μm0.5.

Effect of Scandium on Homogenization Treatment and Friction Stir Processing on Mechanical Properties of 7075 Aluminium Alloy Prepared by Foundry Route

The aluminium alloy (7075 series) with minor scandium (Sc) addition prepared by foundry route, was subjected to homogenization treatment at different temperatures from 300 to 500°C for 8h and also multi-pass friction stir processing (MP-FSP) was performed to improve surface properties of cast aluminium alloy. The effect of minor scandium (0.33wt.%) on the microstructure and mechanical properties of prepared alloy was investigated using optical microscopy, SEM, FESEM, XRD, TEM, Vickers’s hardness and tensile test. The homogenized microstructure was obtained showing fine grains because homogenization of cast structure and dispersion of second-phase particles also occur. The Al-Zn-Mg alloy with high strength, good corrosion resistance and good welding property is used widely in various industrial applications. In addition of scandium to increase the strength mainly comes from fine grain strengthening, substructure strengthening and precipitation strengthening caused by Al3 (Sc) and MgZn2 particles. These particles are formed during homogenization treatment of cast aluminium alloy and it has great influence on precipitation behaviour of Al3 (Sc) particles

Effect of Scandium on Homogenization Treatment and Friction Stir Processing on Mechanical Properties of 7075 Aluminium Alloy Prepared by Foundry Route

The aluminium alloy (7075 series) with minor scandium addition prepared by foundry route, was subjected to homogenization treatment at different temperature from 300 to 500°C for 8h and also multi-pass friction stir processing (MP-FSP) was performed to improve surface properties of cast aluminium alloy. The effect of minor scandium (0.33wt.%) on the microstructure and mechanical properties of prepared alloy was investigated using optical microscopy, SEM, FESEM, XRD, TEM, Vicker’s hardness and tensile test. The homogenized microstructure was obtained showing fine grains because homogenization of cast structure and dispersion of second-phase particles also occur. The Al-Zn-Mg alloy with high strength, good corrosion resistance and good welding property is used widely in various industrial applications. In addition of Sc to increase the strength mainly comes from fine grain strengthening, substructure strengthening and precipitation strengthening caused by Al3(Sc) and MgZn2 particles. These particles are formed during homogenization treatment of cast aluminium alloy and it has great influence on precipitation behaviour of Al3(Sc) particles.

Effect of tempering on microstructure and mechanical properties of a Ta-added 9%Cr steel with high B and low N contents

Ta was added to a modified 9%Cr steel with high B and low N content to achieve an optimal dispersion of second phase particles. The effect of tempering on the microstructure and mechanical properties of an Fe-0.1C-9Cr-1.8W-0.6Mo-3Co-Nb-V-0,0013B-0,007N-0,085Ta steel was investigated. Typical martensite lath structure was observed after normalization at 1323 K for 0.5 h. The M23(C,B)6 and complex (Nb,Ta)(C,N) particles formed during tempering at 1023-1053 K. An increase in the hardness after tempering at 1038 K was attributed to the precipitation of the fine (Nb,Ta)(C,N) particles. The impact toughness depended significantly on tempering temperature. The impact toughness increased from 25 to 181 J/cm2 with increasing the tempering temperature from 1038 to 1053 K.

Comparative analysis of the microstructures and mechanical properties of Co-Cr dental alloys fabricated by different methods

Statement of problemLimited information is available regarding the microstructures and mechanical properties of Co-Cr dental alloys prepared using conventional casting (CAST), computer numerical control (CNC) milling, and selective laser melting (SLM). PurposeThe purpose of this in vitro study was to evaluate the mechanical properties and microstructures of Co-Cr dental alloys fabricated using conventional casting, computer numerical control milling, and selective laser melting and to estimate the potential of applying the SLM technique in prosthetic dentistry. Material and methodsEach group (n=6) of 50-mm-long Co-Cr alloy, dumbbell-shaped specimens was fabricated using the CAST, CNC, and SLM techniques. For each technique, the corresponding commercial alloy material was used. The mechanical properties were evaluated using a tensile test according to International Organization for Standardization (ISO) standard 6892, including 0.2% yield strength, ultimate tensile strength, elongation, and fracture analysis. The microstructures of the specimens were evaluated by using metallurgical microscopy, X-ray diffraction (XRD), and scanning electron microscopy. The Tukey honest significant difference test (α=.05) was used to statistically analyze the 0.2% yield strength, ultimate tensile strength, and microhardness values. ResultsThe microstructures of the SLM specimens exhibited homogeneously distributed fine grains, dispersed second-phase particles, and few defects, and the XRD results showed the α-Co phase predominated, with minimal ε-Co phase and no harmful needle σ phase in the SLM group. The mean ±standard deviation of the 0.2% yield strength of the SLM specimens was 790 ±11 MPa, and the ultimate tensile strength was 1072 ±18 MPa. These values exceeded those of the CAST and CNC specimens by approximately 50% (P<.05). The SLM group showed the highest microhardness (475.3 ±10.2 HV10), followed by the CNC (325.2 ±17.8 HV10) and CAST group (323.7 ±27.2 HV10). Additionally, the ductility and toughness of the SLM specimens were also better than those of the other 2 groups. No significant differences were found in the mechanical performance between the CNC and CAST specimens (P>.05). ConclusionsThe microstructures and mechanical properties of Co-Cr dental alloys were dependent on the fabrication techniques. The SLM specimens exhibited better microstructures and mechanical properties than those fabricated with CNC or CAST.

Influence of Sintering Temperature on Hardness and Wear Properties of TiN Nano Reinforced SAF 2205

Conventional duplex stainless steel degrade in wear and mechanical properties at high temperature. Attempts have been made by researchers to solve this problems leading to the dispersion of second phase particles into duplex matrix. Powder metallurgy methods have been used to fabricate dispersion strengthened steels with a challenge of obtaining fully dense composite and grain growth. This could be resolved by appropriate selection of sintering parameters especially temperature. In this research, spark plasma sintering was utilized to fabricate nanostructured duplex stainless steel grade SAF 2205 with 5 wt.% nano TiN addition at different temperatures ranging from 1000 °C to 1200 °C. The effect of sintering temperature on the microstructure, density, hardness and wear of the samples was investigated. The results showed that the densities and grain sizes of the sintered nanocomposites increased with increasing the sintering temperature. The microstructures reveal ferrite and austenite grains with fine precipitates within the ferrite grains. The study of the hardness and wear behaviors, of the samples indicated that the optimum properties were obtained for the sintering temperature of 1150 °C.

Lattice Boltzmann models for the grain growth in polycrystalline systems

In the present work, lattice Boltzmann models are proposed for the computer simulation of normal grain growth in two-dimensional systems with/without immobile dispersed second-phase particles and involving the temperature gradient effect. These models are demonstrated theoretically to be equivalent to the phase field models based on the multiscale expansion. Simulation results of several representative examples show that the proposed models can effectively and accurately simulate the grain growth in various single- and two-phase systems. It is found that the grain growth in single-phase polycrystalline materials follows the power-law kinetics and the immobile second-phase particles can inhibit the grain growth in two-phase systems. It is further demonstrated that the grain growth can be tuned by the second-phase particles and the introduction of temperature gradient is also an effective way for the fabrication of polycrystalline materials with grained gradient microstructures. The proposed models are useful for the numerical design of the microstructure of materials and provide effective tools to guide the experiments. Moreover, these models can be easily extended to simulate two- and three-dimensional grain growth with considering the mobile second-phase particles, transient heat transfer, melt convection, etc.