Grain Size Of Alloy Research Articles

Microstructure, anticorrosion, biocompatibility and antibacterial activities of extruded Mg−Zn−Mn strengthened with Ca

To find suitable biodegradable materials for implant applications, Mg−6Zn−0.3Mn−xCa (x=0, 0.2 and 0.5, wt.%) alloys were prepared by semi-continuous casting followed by hot-extrusion technique. The microstructure and mechanical properties of Mg−6Zn−0.3Mn−xCa alloys were investigated using the optical microscope, scanning electron microscope and tensile testing. Results indicated that minor Ca addition can slightly refine grains of the extruded Mg−6Zn−0.3Mn alloy and improve its strength. When 0.2 wt.% and 0.5 wt.% Ca were added, the grain sizes of the as-extruded alloys were refined from 4.8 to 4.6 and 4.2 μm, respectively. Of the three alloys studied, the alloy with 0.5 wt.% Ca exhibits better combined mechanical properties with the ultimate tensile strength and elongation of 334 MPa and 20.3%. The corrosion behaviour, cell viability and antibacterial activities of alloys studied were also evaluated. Increasing Ca content deteriorates the corrosion resistance of alloys due to the increase of amount of effective cathodic sites caused by the formation of more Ca2Mg6Zn3 phases. Cytotoxicity evaluation with L929 cells shows higher cell viability of the Mg−6Zn−0.3Mn−0.5Ca alloy compared to Mg−6Zn−0.3Mn and Mg−6Zn−0.3Mn− 0.2Ca alloys. The antibacterial activity against Staphylococcus aureus is enhanced with increasing the Ca content due to its physicochemical and biological performance in bone repairing process.

Improved mechanical, bio-corrosion properties and in vitro cell responses of Ti-Fe alloys as candidate dental implants

A comprehensive study of Fe alloying influence on as-cast titanium alloys, including microstructure, mechanical properties, bio-corrosion behavior and in-vitro cell response have been carried out to evaluate the biological application potential of Ti-Fe binary alloys. The results indicate that grain sizes of as-cast Ti-Fe alloys are remarkably refined with Fe addition and the mechanical strength is increased tremendously. For instance, Ti-2Fe alloy presents excellent mechanical properties by elevating the tensile strength to 566 MPa, or 1.5 times over pure Ti, while maintaining a relative high plasticity. All Ti-Fe alloys carried in this study show a higher corrosion resistance in Hank's solution than pure Ti due to the grain refine enhancement and higher oxide film growth kinetics. Ti-2Fe alloy presents the best corrosion resistance among them and higher Fe content could bring more Fe2O3 to the oxidation films that decrease the corrosion resistance accordingly. All Ti-Fe alloys are holding a similar osteoblast cell viability and response to pure Ti which ensure their biocompatibility. The combination of mechanical properties, corrosion resistance and in-vitro response of Ti-2Fe promised its application as dental implants in a near future.

Microstructural evolution and superplastic behavior of a fine-grained Mg−Gd−Y−Ag alloy processed by simple shear extrusion

Abstract Two magnesium alloys with the nominal compositions of Mg−6Gd−3Y (GW63) and Mg−6Gd−3Y−1Ag (GW63−1Ag) were hot extruded and then processed by 6 passes of the simple shear extrusion (SSE) process at 553 K. Both SEM and EBSD studies confirmed the mean grain size reduction of the extruded base GW63 alloy from 10.1 to 2.9 μm by adding 1 wt% Ag. This decrease in the grain size was due to the formation of the Ag-containing precipitates with network-type morphology at the grain boundaries of the extruded GW63−1Ag alloy. Further grain refinement was achieved after SSE through the occurrence of DRX in both Ag-free and Ag-containing alloys. However, the GW63−1Ag alloy showed a higher fraction of DRX grains and HAGBs after SSE processing compared to the Ag-free alloy. The enhanced DRX behavior was attributed to the smaller initial grain size of the Ag-containing alloy in the as-extruded condition and the role of Ag addition in suppressing the solute drag effect of the segregated Gd and Y elements at the grain boundaries. The superplastic behavior of the alloys was assessed via the shear punch testing (SPT) method performed in the temperature ranges of 623–723 K for the extruded specimens and 573–673 K for the SSE processed alloys. It was revealed that none of the extruded alloys exhibited superplastic flow, because of their large grain sizes. The GW63 alloy processed by 6 passes of SSE displayed a maximum m-value of 0.38 at 648 K, while the high strain rate sensitivity (SRS) index of 0.5 was measured at 623 K for the Ag-containing alloy after SSE. This was accompanied with a superplastic deformation behavior of the latter alloy, for which an activation energy of 105 kJ mol−1 that is close to that of the grain boundary diffusion of pure Mg was obtained. Therefore, grain boundary sliding (GBS) associated with grain boundary diffusion was introduced as the dominant deformation mechanism during the superplastic flow of the Ag-containing alloy processed by SSE.

Effect of Al-3 wt% Al2O3 master alloy fabricated by calcined kaolin on grain refinement and mechanical properties of A356 alloy

In the present study, Al-3 wt% Al2O3 master alloy was successfully prepared by the reaction between calcined kaolin and aluminum melt, combined with mechanical stirring and high-energy ultrasonic dispersion technology. The γ-Al2O3 particles produced by the reaction are uniformly dispersed in the matrix, and the average size of γ-Al2O3 is about 65 nm. The refinement effect of Al-3 wt% Al2O3 master alloy on A356 alloy was studied. It was found that the α-Al grain size in A356 alloy refined by Al-3 wt% Al2O3 master alloy was decreased from 980 ± 155 µm to 337 ± 95 µm. Compared with the Al-5Ti-1B master alloy, Al-3 wt% Al2O3 has a higher refinement efficiency. In addition, the refinement efficiency of the Al-3 wt% Al2O3 master alloy will not fade within 60 min. Transmission electron microscope analysis showed that the orientation relationship between γ-Al2O3 and Al was (22−2)γ-Al2O3[011]γ-Al2O3//(11−1)Al[011]Al, which demonstrated that γ-Al2O3 could be used as heterogeneous nucleation sites to refine α-Al grains. Moreover, the tensile properties of A356 alloy had been significantly improved.

Study of Microstructure Features and Properties of Metals Obtained by Hot Isostatic Pressing

The aim of this research is to study the features of the structure and properties of alloys obtained using the technology of hot isostatic pressing (HIP) of metal powders. The study was carried out in the temperature range of interruption of the HIP cycle from 670 to 1150 °C on alloys 08Cr18Ni10Ti and Cr12MoV. For processing images of microstructures and assessing their fractal dimension, software has been developed in the MATLAB environment. The results of microstructural analysis of the metals under study showed that complete sintering of powders is observed at a HIP temperature of 1150 °C; at lower temperatures, pores and unsintered spherical particles of metal powder are observed in the microstructure of the alloys. The grain size of alloys obtained by HIP is determined, first of all, by the size of the initial fraction of the metal powder. Based on the results of evaluating the density of alloys obtained at different temperatures of the HIP, a relationship was established between the relative density of the alloy and the process temperature. Based on the results of fractal analysis, the relationship between the fractal dimensionality of the microstructure of the alloy and the HIP temperature and the relative density of the metals under study has been established. The obtained dependences are linear. The error in estimating the relative density from the obtained dependencies is, on average, 5 %. The data obtained in the course of the study make it possible to estimate the density of metals obtained by hot isostatic pressing of metal powders by evaluating the fractal dimension of the microstructure image.

The Role of Binding Phase in Hard Alloys (Analytical Review)

A review of articles on the influence of the composition and structure of the binding phase on the properties of hard alloys is given. The role of the binding phase influencing the properties of hard alloys on the basis of data of domestic and foreign researchers is emphasized. The existing and new data on testing of the elements of periodic system as a binding phase which impacts the microstructure and properties of a hard alloy are presented. The existing and new proposals on replacing of the main element (cobalt) with iron, nickel, rhenium, molybdenum, chromium, etc., are considered in order to obtain higher properties and lower the price of the alloy. It is shown that obtaining the best operational properties in each particular case of application of the alloy requires an optimal combination of grain size and cobalt content. Various hard-alloy products are indicated for different areas of application. Techniques of reinforcement of the binding of hard alloys by means of introduction of various types of reinforcers are considered. Their influence on average grain size and properties of hard alloy is shown by examples of various grain growth inhibitors. The ways of further development of submicron, ultrathin, and nanophase alloys with a nanostructured binder reinforced with nanoparticles are presented. The way of further development of hard alloys is shown by example of alloy WC–50% Со with additions. The properties of replacing the cobalt binder with nickel alloyed with small additives are indicated: Мо, W, TiC, HfC, VC, NbC, TaC, Cr3C2.

Modeling of Dynamic Recrystallization Behavior of As-Extruded AM50 Magnesium Alloy during Hot Compression by a Cellular Automaton Method

The dynamic recrystallization (DRX) behavior of as-extruded AM50 magnesium alloy was modelled and simulated by a cellular automaton (CA) method. Isothermal compression experiments were conducted, and the characteristic parameters in the CA model were obtained by the testing stress–strain flow curves in a wide temperature range of 250–450 °C and strain rate range of 0.001–10 s−1. The flow stress, DRX volume fraction and DRX grain size of the as-extruded AM50 magnesium alloy were predicted by CA simulation. The results showed that the DRX behavior of the studied magnesium alloy was susceptive with the temperature and strain rate; meanwhile, the prediction results were approximate to the experimental values, indicating that the developed CA model can make a confident estimation on the DRX behavior of the as-extruded AM50 magnesium alloy in high temperature conditions.

Evaluating compressive property and hot deformation behavior of molybdenum alloy reinforced by nanoscale zirconia particles

The paper deals with the fabrication of molybdenum alloy bars with different ZrO2 content via a series of processes, involving hydrothermal synthesis, co-precipitation, co-decomposition, powder metallurgy and rotary swaging. The compressive properties of molybdenum alloy bars were tested at various temperatures from room temperature to 1400 °C, and hot deformation behavior at different temperatures and strain rates was studied. The results show that ZrO2 particles with the size of tens of nanometers are evenly dispersed in Mo matrix, and ZrO2(110) and Mo(110) have a non-coherent interface due to a larger lattice misfit 13.57%. ZrO2 particles could significantly reduce grain size of molybdenum alloy and improve its compressive properties. When the volume content of zirconia increases from 0% to 2.0%, the grain size of molybdenum alloys annealed at 1200 ℃ decreases sharply from 55.9 µm to 3.5 µm. The compressive yield strength (CYS) of Mo-2.0 vol%ZrO2 annealed at 1200 °C is 674 MPa at room temperature, which is 65.6% higher than that of pure Mo. The high temperature CYS of Mo-2.0 vol% ZrO2 at 1400 °C is 176 MPa, increasing 49.6% higher than that of pure Mo. Compared with the previous works, the peak flow stress of the new Mo-2.0 vol%ZrO2 has been significantly improved. Adding of 2.0 vol%ZrO2 increases the initial temperature of dynamic recrystallization to 1200 °C, and effectively prevents the grain growth of dynamic recrystallization even at the increased deformation temperature of 1400 °C.

Effect of Sn addition on the microstructure and mechanical properties of AZ31 alloys

An Mg-3Al-1Zn-xSn (x = 0, 3, 6, 9) alloy was prepared by die-casting and analyzed by XRD, SEM, and EBSD. The microstructure, second phase, and grain orientation of the AZT31x alloy were characterized. As the Sn content increased from 3 wt.% to 9 wt.%, the tensile and yield strength of the alloy were effectively improved. With the addition of Sn, the grain size of alloys decreases gradually blocking the dislocation by the grain boundary and the dispersion of the Mg2Sn second phase in the AZT31x(x = 3, 6, 9) alloys contributes to the strength via grain boundary pinning. According to theoretical analysis and calculation, the high strength of AZT319 alloy is partly attributed to the grain fine strengthening ) and second phase strengthening The total increased strengthening value is lower than experimental value (). The ratio about / and / in die-cast alloys tensioned to 0.08 deformation gradually decrease, which can reflect that high-Sn content contributes to the strain hardening behavior. The ductility of AZT313 alloy was lightly improved due to the {10-12} tensile twins. When excessive Sn was added, the Mg2Sn second phase coarsened and acted as the nucleus of micro-cracks during the stretching process, thereby reducing the ductility of the alloy.

Microstructure and compression properties of fine Al2O3 particles dispersion strengthened molybdenum alloy

Abstract The Mo alloys reinforced by Al2O3 particles were fabricated by hydrothermal synthesis and powder metallurgy. The microstructures of Mo−Al2O3 alloys were studied by using XRD, SEM and TEM. The results show that Al2O3 particles, existing as a stable hexagonal phase (α-Al2O3), are uniformly dispersed in Mo matrix. The ultrafine α-Al2O3 particles remarkably refine grain size and increase dislocation density of Mo alloys. Moreover, a good interfacial bonding zone between α-Al2O3 and Mo grain is obtained. The crystallographic orientations of the interface of the Al2O3 particles and Mo matrix are [ 1 ¯ 11 ] α - Al 2 O 3 / / [ 1 ¯ 11 ] Mo and [ 1 1 ¯ 2 ] α - Al 2 O 3 / / [ 0 1 ¯ 1 ] Mo . Due to the effect of secondary- phase and dislocation strengthening, the yield strength of Mo−2.0vol.%Al2O3 alloy annealed at 1200 °C is approximately 56.0% higher than that of pure Mo. The results confirm that the addition of Al2O3 particles is a promising method to improve the mechanical properties of Mo alloys.

Effect of Grain Size of Cu-Zn Alloys on Dislocation-Strengthening Factors

Effect of Grain Size of Cu-Zn Alloys on Dislocation-Strengthening Factors

Triaxial tension-induced damage behavior of nanocrystalline NiTi alloy and its dependence on grain size

This study focused on the effect of grain size (GS) on dynamic damage performance of nano-crystalline nickel titanium (NC NiTi) alloy. Molecular dynamics simulations were conducted to triaxially expand it at a high strain rate (4 × 109 s−1), while the temperature and initial pressure remained 300 K and 0 bar, respectively. It was discovered that the superelastic NiTi alloy exhibited the similar damage response as ductile metallic materials, which was vividly characterized by void nucleation, growth, and coalescence. The stress-strain curves demonstrated that the void nucleations always occurred near the start of the strain softening region at various grain sizes. Interestingly, it was discovered that the void evolution was characteristic of an almost double-linear behavior, and the piecewise linearity became more prominent for the void volume fraction increase at larger grain size. More importantly, the fracture behavior was found to be strongly dependent upon the grain size in the NC NiTi alloy. For small grain size, the existing voids propagated along the grain boundaries and in the grains, leading to intergranular and transgranular fracture. Contrarily, the intergranular-dominated fracture was responsible for the void propagation in the large grain. In addition, the starting time, ending time, and threshold of void nucleation were found to be weak sensitivity to GS, and a reverse effect was appropriate to the void growth. The results highlighted that as the GS increased, more complete stress relaxation and shorter duration time were produced, leading to larger void volume fraction and faster growth rate.

Enhanced mechanical properties in oxide-dispersion-strengthened alloys achieved via interface segregation of cation dopants

With significantly enhanced irradiation resistance, high-temperature strength, and creep resistance, oxide-dispersion-strengthened tungsten (ODS-W) alloys present tremendous potential for high-temperature applications. However, the oxide particles tend to segregate at W grain boundary and grow up (even to micron), greatly suppressing their strengthening effect. It is always a great challenge to effectively refine and disperse the oxide particles at W grain boundary. Here, we successfully developed a new type of cation-doped W-Y2O3 alloy via a wet chemical method and subsequent low-temperature sintering. It was found that proper cation doping could not only significantly refine the intergranular Y2O3 second phase particles but also dramatically improve the sinterability of W matrix. These doping effects, as a result, simultaneously enhance the strength and ductility of the W-Y2O3 alloy. It was confirmed that the segregation of cation dopants at the W/Y2O3 interface is the origin of these doping effects. Furthermore, X-ray photoemission spectra (XPS) analyses confirmed that cation dopant segregation also obviously affects the chemical bonding (i.e., W-O bond) along the W/Y2O3 interface. As a result, the rate-limiting mechanism for W grain growth is influenced remarkably, explaining well the difference of W grain size in various cation-doped W-Y2O3 alloys. For the refinement of intergranular Y2O3 particles, it can be understood well from both thermodynamic and kinetic views. Detailedly, W/Y2O3 interfacial energy and atom mobility for Y2O3 coarsening are all limited by cation dopant segregation. More importantly, this cation-doping approach can also be applicable to other ODS alloys for enhancing their comprehensive mechanical properties.

Effect of different casting techniques on the microstructure and mechanical properties of AE44-2 magnesium alloy

AE44-2 magnesium (Mg) alloys were fabricated by gravity casting (GC), high pressure die casting (HPDC), and high vacuum assisted high pressure die casting (HVHPDC). The effect of these three different casting techniques on the microstructure evolution, texture, and mechanical properties of the AE44-2 alloy was investigated. The results showed that the different cooling rates in these three different casting techniques led to the different distribution and morphology of the precipitated phases, and rapid cooling contributed to a dense network distribution of the phases as well as grain refinement. In addition, the faster cooling rate resulted in a decrease of the dislocation accumulation. The addition of vacuum assistance in the HPDC process increased texture strength. The average grain size of the HPDC alloy was reduced by 90.4% compared to the GC alloy and the yield strength increased by 85.7 MPa due to rapid cooling. The elongation of the HVHPDC alloy increased by 2.3% compared to the HPDC alloy due to vacuum assistance. Moreover, the mechanical properties improved for the alloys in the order of GC < HPDC < HVHPDC because of gran refinement caused by the faster cooling rate. Based on the analysis of the strengthening mechanisms, the rapid cooling process of the HPDC alloy led to better strengthening compared to the GC alloy. In addition, grain refinement contributed to 82.1% of the strengthening mechanism.

Rapid solidification microstructure evolution and grain refinement of deeply undercooled nickel alloys

High undercoolings of Ni75Cu25, Ni70Cu30 and Ni65Cu35 alloys were achieved by combined methods of cyclic superheating and molten glass purification. The average grain size of the undercooled alloys was decreasing with increasing Cu atomic percent. In the obtained undercooling ranges, it could be found that there were two grain refinement events at low undercoolings and high undercoolings. The grain refinement at low undercoolings was caused by dendrite remelting, while high-angle grain boundary and annealing twins indicated that recrystallization had occurred at high undercoolings. Applying TEM method, it was found that many dislocations and twins were present in the substructure at high undercoolings. The microhardness of Ni65Cu35 alloy with undercooling was sharply decreased at the critical undercooling confirmed that the stress accumulated in the microstructure at high undercoolings was consumed due to recrystallization process.

Effects of Mo content on the grain size, hardness and anti–wear performance of electrodeposited nanocrystalline and amorphous Ni–Mo alloys

NiMo alloys with various Mo contents are prepared by electrodeposition in sulfate–citrate acid solutions under different temperature, pH, stirring rate, current density and MoO42− concentration. Influences of Mo content on the grain size, hardness and wear resistance are studied. Results show that the increase in Mo content decreases the deposition rate of NiMo alloys prepared at a constant temperature. As–prepared alloys are composed of nanocrystalline Ni(Mo) solid solution when Mo is less than 24.4 at.%. The grain size of alloys decreases with the increment of Mo content. Amorphous phase appears in deposits when Mo content exceeds 24.4–27.3 at.%. Hardness and wear resistance of alloys firstly increases with Mo content, and then it has a decline due to the formation of amorphous. Additionally, Hall–Petch (HP) relationship is found in deposits as the grain size decreases from 12.4 nm to 7.9 nm, and then the inverse HP relationship appears with the further decrease in grain size to 1.5 nm. Meanwhile, traditional Archard law is found in NiMo alloys with Mo content in the range of 6.3–27.3 at.%. Additionally, HP breakdown causes a variation of wear resistance at the critical grain size of 7.9 nm.

Influence of Solution Treatment Temperature on the Microstructure of Ni-based HR-120 Superalloy

The solution treatment process has been carried out on Ni-based HR-120 superalloy (Fe-40Ni-24Cr) at six different temperatures, namely 950ºC, 1000ºC, 1050ºC, 1100ºC, 1150ºC and 1200ºC. All samples were soaking for 3 hours at desired temperature, followed by water quench. The main objective of the solution treatment process is to vary the grain size of the alloy. The effect of solution treatment process on the alloy has been investigated in term of microstructure, grain size, phase present and hardness test, by using optical microscope, scanning electron microscope (SEM) equipped with energy dispersive x-ray (EDX) spectrometer, x-ray diffraction (XRD) technique and Vickers hardness test. As a results, the grain size of the solution-treated alloy were increase as the solution treatment temperature increase from 27.27 μm to 40.86 μm for solution-treated alloy at 950ºC to 1200ºC, respectively. Three precipitate phases were detected during phase analysis which are NbC, TiC and (Nb,Ti)C on the solution-treated alloy. In addition, as the grain size increase when the solution treatment temperature increase, the hardness value was decrease.

Microstructure modification and precipitation strengthening for Mg–6Zn–1Mn–4Sn–0.5Ca through extrusion and aging treatment

Abstract The microstructure revolution and mechanical properties of as-extruded and peak-aged Mg–6Zn–1Mn– 4Sn–0.5Ca (ZMT614–0.5Ca) alloy were studied by OM, SEM, TEM, hardness testing and tensile testing. The results showed that the as-cast ZMT614–0.5Ca alloy mainly consisted of α-Mg, Mg–Zn and CaMgSn phase. The hot extrusion process effectively refined the microstructure and led to a completely dynamic recrystallized microstructure. The average grain size of as-extruded alloy was ˜4.85 μm. After solution treatment, remained CaMgSn with high melting point played a significant role in pinning effect and impeding the migration of grain boundary. After aging treatment, peak-aged ZMT614–0.5Ca alloy exhibited a good combination of strength and ductility, with yield strength, ultimate tensile strength and elongation being 338 MPa, 383 MPa and 7.5%, respectively. The yield strength of the alloy increased significantly by around 36% compared with that in as-extruded condition, which should be attributed to the precipitation strengthening of β' phase.

Grain refinement of Mg-Al alloys inoculated by MgAl2O4 powder

As a potent nucleating substrate for α-Mg grain, MgAl 2 O 4 powder was used to inoculate the Mg-Al melt in this study. The effects of MgAl 2 O 4 amount, holding time and Al content on the grain size and grain refining ratio of the inoculated Mg-Al alloys are systematically investigated. The results show that the minimum grain size of Mg-3Al alloy is achieved by adding 2 wt.% MgAl 2 O 4 powder and this alloy exhibits higher grain refining ratio than Mg-5Al and Mg-8Al alloys. The crystallographic misfit calculation indicates the well-matching and possible orientation relationships (ORs) between α-Mg and MgAl 2 O 4 . Among these predicted ORs, [10–10] α − Mg //[110] MgAl 2 O 4 in (0002) α − Mg //(1–13) MgAl 2 O 4 possesses the smallest misfit, i.e., 2.34% ( f r ). Both results of the experiment and crystallographic calculation demonstrate that the grain refinement of Mg-Al alloys is attributed to the MgAl 2 O 4 particles acting as the heterogeneous nucleation substrates for α-Mg grains.

Investigation of the grain refining performance of Al‐5Ti‐1B master alloy on the recycling process of A356 alloy

AbstractIn this paper, the grain refining performance of Al‐5Ti‐1B master alloy on the recycled A356 alloy is investigated using the macrostructure examination and chemical analysis. Results show that Al‐5Ti‐1B is composed of the dispersion of blocky TiAl3 particles and mixtures of small TiAl3 and TiB2 particles. Both particles refine grain structures of A356 alloy. As the initial recycling process proceeds, A356 alloy still exhibits fine structures. However, during the subsequent recycling process, the grain size of A356 alloy become larger. The concentration of titanium and boron decreases with increasing the number of recycling, especially in the subsequent recycling process. It is proposed that recycling of refined A356 can best be conducted in the initial recycling process and then additional grain refiner needs to be added to maintain the grain refining performance for the continuous recycling process of A356 alloy.