Room Temperature Compressive Properties Research Articles

Microstructure, Compressive Properties and Oxidation Behaviors of the Nb-Si-Ti-Cr-Al-Ta-Hf Alloy with Minor Holmium Addition

In the present research, the Nb-Si-Ti-Cr-Al-Ta-Hf alloys with different Ho addition were prepared. Their microstructure, compressive properties and oxidation behaviors were investigated preliminarily. The results exhibit that the Nb-Si-Ti-Cr-Al-Ta-Hf alloy has coarse microstructure which is mainly composed of Nb solid solution, Nb5Si3 and Ti5Si3 phases. The minor Ho addition could refine the microstructure and suppress the precipitation of Ti5Si3 phase. Moreover, the Ho addition also leads to the formation of Ho2Hf2O7, which prefers to precipitate along the Nbss/Nb5Si3 phase interface. Compared with the Nb-Si-Ti-Cr-Al-Ta-Hf alloy, the minor Ho addition improves the room-temperature and high-temperature compressive properties of the alloy. Its room-temperature compressive strength and ductility obtain the maximum value of 1825 MPa and 16.5% when the Ho content is 0.1 at.%. Moreover, its best compressive strength at 873 K, 1273 K and 1473 K is 1495 MPa, 765 MPa and 380 MPa, respectively, when the Ho addition is 0.1 at.%. The oxidation behavior of the Nb-Si-Ti-Cr-Al-Ta-Hf alloy is diversified with the Ho addition. The oxidation rate of the alloy with 0.1 at.% Ho addition is the lowest while the alloy with 0.2 at.% Ho addition is the highest. Therefore, the 0.1 at.% Ho would be the appropriate content for the Nb-Si-Ti-Cr-Al-Ta-Hf alloy.

In-situ TiC/Ti composites based on Ti2AlC–Ti system: Reaction process, microstructure, and mechanical properties

Based on the improvement of the phase transition temperature of Ti by Al element and the excellent strengthening effect of TiC particles, this paper selects Ti2AlC as the precursor, striving to improve the high-temperature performance of the Ti matrix. The composites with 1–10 vol% Ti2AlC addition were fabricated by hot-pressing sintering. And a detailed study was conducted on the reaction process, microstructure, room and high temperature compression properties of the composites. The experimental results show that the separation of Al elements at the A-position occurs at around 700 °C in Ti2AlC, and the Al element is homogenized in the matrix during the subsequent sintering process. Micron sized TiC particles are mainly distributed at the Ti grain boundaries, while the content of sub-micron sized TiC particles entering the crystal increases with the increasing Ti2AlC addition. The interface mismatch between TiC and Ti is small, and the bonding is well. These microstructures enable composite materials to exhibit excellent mechanical properties, with 10 vol% Ti2AlC/Ti composite having a yield strength of 1858 MPa and an ultimate strength of 2200 MPa at room temperature, and maintaining a yield strength of 602 MPa and an ultimate strength of 1264 MPa at 500 °C.

Microstructures and mechanical properties of novel MoTaVW refractory high-entropy alloys

Refractory high-entropy alloys (RHEAs) containing multiple principal alloying elements have created a growing interest in exploring superalloys applications due to their high melting points and excellent softening resistance. The room-temperature brittleness and oxygen sensitivity greatly restrict their further processing and application. Here, utilizing the unique high strength of Vanadium (V) among alloy elements and cocktail effect of HEAs, we designed a MoTaVW RHEAs with equal atomic ratio, that exhibit multiphase phases (Ta-rich, Mo-rich and V-rich phase) with different composition at different sintering temperatures and the alloy elements in BCC solid solution tend to be uniformly distributed as the increased sintering temperature. Exploring the room-temperature compressive properties and underlying deformation mechanisms, the MoTaVW RHEAs exhibit the yield strength (σy) of 1420 MPa and the plastic strain (εp) of 18 %, that achieved good combination of strength and plasticity compared with other most known BCC RHEAs, which are attributed to high solid solution strengthening caused by lattice distortion and the cross slip of screw dislocations on the close-packed plane that can enhance the synergistic effect of strength and plasticity. These results reveal the MoTaVW RHEAs is a very promising materials for compositional space in RHEAs.

Effect of continuous multistep hydrogenation treatment step on microstructures and room-temperature compressive properties of TC21 alloy

The effect of continuous multistep hydrogenation treatment (CMHT) step on the microstructure of TC21 alloy was investigated by OM, XRD and TEM. Compressive properties of CMHT-processed TC21 alloys under diverse compressive velocities were also studied through room-temperature compression experiments. Results showed that the amount of α phase decreased and the amount of β phase and δ hydride increased as the CMHT step increased. α’ martensite occurred only in TC21 alloy processed by one step CMHT. The deformation limit of CMHT-processed TC21 alloys showed the same change law under diverse compressive velocities, which decreased first, then increased, and finally decreased again as the CMHT step increased. The maximum increase of the deformation limit of TC21 alloy after CMHT reached 93.96% as compared to the original TC21 alloy. Reasons for the change of compressive properties of TC21 alloy processed by CMHT were analyzed.

MoNbV, MoNbVTi and MoNbVTiHf multicomponent refractory alloys—Compositional modulated mechanical properties investigating

In this paper, equiatomic MoNbV, MoNbVTi and MoNbVTiHf refractory multi-component alloys were investigated in comparative style. Single body centered cubic (BCC) structure with increased lattice parameter were determined by X-ray diffraction. Typical dendrite structure was demonstrated by scanning electronic microscope. Mechanical testing shows excellent room temperature compressive mechanical properties of MoNbVTi high entropy alloy (HEA), which exhibited maximum compressive strength beyond 2000 MPa and the fracture strain exceeds 25 %. The high temperature compressive testing shows outstanding high temperature softening resistance of MoNbV medium entropy alloy (MEA), which exhibited compressive strength above 1160 MPa, and plasticity ductility exceeds 18 % at 1273 K. The present study implies MoNbV MEA possesses excellent high temperature strength and plastic ductility,which shed light on the design of high temperature structural material with simple composition.

On the structure-properties relationship of amorphous and crystalline silica nanoparticles reinforced magnesium matrix nanocomposites

In this study, the structure-properties relationship of magnesium matrix nanocomposites was studied. Using an accumulative extrusion (AE) process, the matrix was reinforced by adding 0.25, 0.5 and 1 wt% crystalline and amorphous silica nanoparticles separately. The mechanical behavior of nanocomposite strips was investigated by hardness and uniaxial compression tests. The results indicated that the Mg/0.5%SiO2-Am had the best room temperature compressive properties. An increase of 28.5% in compressive yield strength after extrusion and 235% after annealing was measured. Ultimate compressive strength (UCS) was increased by 20% without reduction in the nanocomposite ductility compared to the pure magnesium strip. FESEM and OM were used for microstructural analysis and revealed no visible cracks or distinct defects between magnesium layers after AE passes. It is found from the EDS analysis that the reinforcement distribution after the AE process was uniform with few agglomerates. Texture analysis using X-ray diffraction and EBSD after the AE process for samples reinforced with 0.5 wt% of amorphous and crystalline silica nanoparticles indicated a negligible difference in the basal plane orientation of the monolithic and nanocomposite magnesium strips after the AE process along extrusion direction. On the other hand, increasing the basal plane peak intensity after annealing for the sample reinforced with amorphous silica compared to the sample reinforced with crystalline silica indicated a weakening of basal texture. Furthermore, the EBSD analysis showed that amorphous silica nanoparticles are more effective than crystalline silica in grain refinement.

Room-temperature compressive properties of TC21 alloy processed by thermohydrogen treatment at 1123 K

The influence of hydrogen level on compressive properties of TC21 alloy processed by thermohydrogen treatment (THT) at 1123 K was studied through room-temperature compression experiments. The microstructures of TC21 alloy processed by THT at 1123 K were investigated by OM, XRD, and TEM. Results showed that hydrogen level affected apparently the microstructures and compressive properties of TC21 alloy processed by THT at 1123 K. With increasing level of hydrogen, the yield strength of TC21 alloy decreased to a minimum initially and then increased; the deformation limit of TC21 alloy decreased slightly to a minimum first, then increased to a maximum, and ultimately decreased. At a hydrogen level of 0.78 wt%, the deformation limit of TC21 alloy was the highest among all THT-processed TC21 alloys and showed an increase of 244.33% compared with the original TC21 alloy.

Properties of TiCp/Cu composites fabricated by powder metallurgy and electrodeless copper plating

In situ spherical TiCp-reinforced copper matrix composites were prepared via hot-pressing sintering assisted with copper plating. Brinell hardness and electrical conductivity of composites with various contents were investigated, room temperature compression properties and fractography of optimal TiCp/Cu composites and sintered pure copper were analysed. It was found that with the increase of TiCp content, Brinell hardness of composites was increased, while electrical conductivity decreased. When TiCp content was 1.0 wt-%, the Brinell hardness increased significantly and the conductivity was maintained at a high level. Compared with sintered pure copper, the yield strength and ultimate compressive strength of the composites were improved, while the fracture strain was reduced.

Development of single-phase bcc UHfNbTi high-entropy alloy with excellent mechanical properties

Based on the theory of mixing enthalpy of i,j element pairs (ΔHij) and atomic-size difference δ, we designed a uranium-containing equiatomic UHfNbTi high-entropy alloy with a single-phase bcc structure. The alloy showed good room-temperature compressive plastic properties. They with stood at least 60% of compression strain without fracture. We investigated the effect of average valence electron concentration (VEC) on the mechanical properties of the alloy. Reducing the VEC number is expected to produce uranium-containing high-entropy alloys with high ductility.

Correlations to improve room temperature ductility of refractory complex concentrated alloys

Room temperature tensile and compressive properties of refractory complex, concentrated alloys (RCCAs) have been analyzed to explore correlations capable of anticipating ductility in this growing class of structural materials. The Pugh-Pettifor and Rice-Thomson ductility criteria are generally satisfied by the current dataset, but the dataset does not cover a sufficiently wide range to provide a critical evaluation. A previously suggested ductility criterion based on the average valence electron concentration (VEC) of an alloy, i.e. abrupt ductile to brittle transition at VEC = 4.5, is not supported in the present study. A revised VEC criterion is suggested, but the data supporting this trend is sparse and additional work is needed. These three ductility criteria are evaluated using only single-phase RCCA data. A new ductility criterion based on the RCCA yield strength (σy) is suggested from the present work, using both single-phase and multi-phase data. RCCAs with commercially relevant tensile ductility have σy ≤ 1200 MPa, and alloys with compressive ductility of ≥30% (analyzed here to provide useful tensile ductility) have σy ≤ 1500 MPa. Strengthening models to predict σy in RCCAs may thus be used to anticipate alloys that may also possess useable levels of ductility.

Investigations on the NiAl–Cr(Mo) eutectic alloy with optimized microstructure and improved room-temperature compressive properties

In this paper, microstructural optimization was chosen to strengthen NiAl-based alloys based on hot pressing sintering of pre-alloyed powders. The Cr(Mo) phase in the eutectic cell was refined to 200 nm successfully. Owing to the growth of the Cr(Mo) phase, the volume fraction of the eutectic cells greatly reduced. The compact sample has been obtained at a relatively lower temperature and an extended holding time to retain the eutectic cells. Each compact sample shows considerable performance both in strength and plasticity for compression test at room-temperature. The grown Cr(Mo) phase which can resist the cracks and the eutectic cells with nano-sized Cr(Mo) phase are the main reasons for toughening and strengthening. The improvement of strength and plasticity of alloy in this paper can provide basic understanding for further development of NiAl-based alloy.

Development of Single-Phase Bcc UHfNbTi High-Entropy Alloy with Excellent Mechanical Properties

Based on the theory of mixing enthalpy of i, j element pairs (ΔH ij) and atomic-size difference δ ， we designed and fabricated a uranium-containing equiatomic UHfNbTi high-entropy alloy with a single-phase bcc crystal structure. The solidified microstructure of the as-cast alloy exhibitsequi-axis fine dendrite and typical columnar crystal structure. The alloy showed good room-temperature compressive plastic properties. They withstood at least 60% of compression strain without fracture. We investigated the effect of average valence electron concentration (VEC) on the mechanical properties of the alloy. Reducing the VEC number is expected to produce uranium-containing high-entropy alloys with high ductility.

Effects of hydrogenation temperature on room-temperature compressive properties of CMHT-treated Ti6Al4V alloy

Compression tests were performed at room temperature to investigate the effects of hydrogenation temperature on compressive properties of Ti6Al4V alloy treated by continuous multistep hydrogenation treatment (CMHT). Pressure-composition isotherms and microstructures were also studied. Results showed that the equilibrium hydrogen pressure increased, and the hydrogen absorption rate decreased with the increase of hydrogenation temperature. The amounts of β phase and α” martensite increased first and then decreased when Ti6Al4V alloy was treated by four times CMHT with the increase of hydrogenation temperature. Hydrogenation temperature played a different role on the compressive properties of CMHT-treated Ti6Al4V alloy. The ultimate compression of Ti6Al4V alloy treated by 11 times CMHT at 850 °C increased by 83.3 % as compared to the as-received Ti6Al4V alloy. The compressive properties of Ti6Al4V alloy were dependent on the amounts of different phases and microstructures when Ti6Al4V alloy was treated by CMHT at different temperatures.

Influence of deep cryogenic cycling on the rejuvenation and plasticization of TiZrHfBeCu high-entropy bulk metallic glass

The effects of deep cryogenic cycling treatment (DCT) on the rejuvenation and room-temperature compressive properties of a TiZrHfBeCu high-entropy bulk metallic glass (HE-BMG) were studied. After DCT, the fully amorphous structure of TiZrHfBeCu HE-BMG remained, but the relaxation enthalpy showed obvious rejuvenation behavior. Upon increasing the number of cycles, the room-temperature plasticity of TiZrHfBeCu HE-BMG gradually increased from 0.62% to 5.38%, with no obvious change in the yield strength. The hardness and density of the high-entropy amorphous alloy decreased with the number of DCT cycles. The DCT-induced rejuvenation and plasticization mechanisms were explained based on the shear transformation zone (STZ) model. The effects of high mixing entropy and fragility on the rejuvenation behavior were also considered. This work confirmed that DCT is an effective method for the rejuvenation and plasticization of TiZrHfBeCu HE-BMG.

Microstructures and room-temperature compressive properties of Ti6Al4V alloy processed by continuous multistep hydrogenation treatment

The effects of continuous multistep hydrogenation treatment (CMHT) on the room-temperature compressive properties of Ti6Al4V alloy were investigated through compression tests. The pressure-composition isotherms of Ti6Al4V alloy hydrogenated at 850 °C with different CMHT numbers were also studied. Results show that CMHT number has different effects on microstructures and compressive properties of Ti6Al4V alloy. When CMHT number increased, the amounts of α phase and α′ martensite decreased, the amount of α″ martensite increased first and then decreased, the number of β phase increased. When the CMHT number was one, δ hydrides precipitated at phase boundary. With the increase of CMHT number, δ hydrides precipitated not only at α phase, but also at β phase. The ultimate compression decreased first up to a minimum, and then increased gradually up to a maximum, finally decreased with the increase of CMHT number. The ultimate compression of Ti6Al4V alloy with eight times CMHT increased by 83.83% as compared to the as-received Ti6Al4V alloy, which was the highest ultimate compression among those of all CMHT-treated Ti6Al4V alloys. Reasons for the distinct effects of CMHT number on the room-temperature compressive properties were discussed.

Microstructures and mechanical properties of Ti–44Al–5Nb–3Cr–1.5Zr–xMo–yB alloys

Abstract

Effects of V addition on the solidification microstructures and room temperature compression properties of NiAl–Cr(Mo) hypereutectic alloy

The solidification microstructures and compression properties of NiAl–32Cr–6Mo and NiAl–36Cr–6Mo hypereutectic alloys with different V additions were studied. The results show that V addition did not change the constitute phase. However, the primary Cr(Mo) phase began to show obvious dendritic morphology, the formation of the eutectic lamellae was disturbed, and the microstructure of the eutectic cell was degraded. The EDS result indicated that all V solubilized in the Cr(Mo) phase. As the V addition increased, the volume fraction of the primary Cr(Mo) phase and the solid solution content of V in the Cr(Mo) phase continued to increase. Due to the solid solution strengthening of V in the alloy, the compression properties of V-doped alloys were obviously improved. Especially, the NiAl–32Cr–6Mo–1V alloy simultaneously had the highest compression strength of 1816 MPa and compression strain of 18.4%. When the V content further increased, although the positive effect due to the solid solution strengthening increased, the increasing number of primary Cr(Mo) dendrites in the alloy would result in decreased compression properties. In addition, all alloys showed brittle quasi-cleavage fracture pattern, while crack bridging, crack deflection and shear ligament were observed in the NiAl–32Cr–6Mo–1V alloy.

Fabrication and Mechanical Properties of Open‐Cell Austenitic Stainless Steel Foam by Electrostatic Powder Spraying Process

An open‐cell metallic foam is newly manufactured using the electrostatic powder spraying (EPS) process, and its room temperature compressive and energy absorption properties are investigated. EPS is a process that uses electrostatic forces. The powder is negatively charged by applying direct current high voltage and undergoes electrostatic spraying on a positively charged polyurethane pre‐form. To control relative density (ρ*/ρ), three different spray amounts are applied (2.5, 3.5, and 4.5 kg m−2). Also, the relative density is measured to increase constantly with the spray amount. The room temperature compressive curves of the EPS foams represent the typical compressive stages (linear elastic, plastic collapse, and densification) of metallic foam. The plateau strengths of the EPS foams measure 0.48 MPa (spraying amount: 2.5 kg m−2), 0.76 MPa (spraying amount: 3.5 kg m−2), and 1.23 MPa (spraying amount: 4.5 kg m−2), respectively. Also, EPS 316L foam with the smallest spray amount has a lower energy absorption amount compared with other types of foam. This study also discusses the compressive and energy absorption behaviors of an open‐cell metallic foam manufactured using the EPS process in relation to its structural and microstructural characteristics.

Room temperature compressive properties and strengthening mechanism of Mg96.17Zn3.15Y0.50Zr0.18 alloy solidified under high pressure

The microstructures of Mg96.17Zn3.15Y0.50Zr0.18 alloys solidified under 2–6 GPa high pressure were investigated by employing SEM (EDS) and TEM. The strengthening mechanism of experimental alloy solidified under high pressure is also discussed by analyzing the compressive properties and compression fracture morphology. The results show that the microstructure of experimental alloy becomes significantly fine-grained with increasing GPa level high pressure during solidification process, and the secondary dendrite arm spacing reduces from 40 μm at atmospheric pressure to 10 μm at 6 GPa pressure. The morphology of the second phases changes from the net structure by the lamellar-type eutectic structure at atmospheric pressure to discontinuous thin rods or particles at 6 GPa pressure. Besides, the solid solubility of Zn in the Mg matrix is improved with the increase of the solidification pressure. Compared with atmospheric-pressure solidification, high-pressure solidification can improve the strength of the experimental alloy. The compressive strength is improved from 263 to 437 MPa at 6 GPa. The fracture mechanism of the experimental alloy changes from cleavage fracture at atmospheric pressure to quasi-cleavage fracture at high pressure. The main mechanism of the strength improvement of the experimental alloy includes the grain refinement strengthening caused by the refinement of the solidification microstructure, the second phase strengthening caused by the improvement of the morphology and distribution of the second phases, and solid solution strengthening caused by the increase of the solid solubility of Zn in the Mg matrix.

A particle reinforced NbTaTiV refractory high entropy alloy based composite with attractive mechanical properties

Refractory high entropy alloys (RHEAs) are promising high temperature structural materials because of their excellent high temperature strength and high melting point. With introducing secondary particles, the high temperature mechanical properties can be further improved. However, its poor ductility limits the industrial application. In the present work, a new ductile NbTaTiV RHEA-based composite reinforced with Ti-C-O particles were in-situ synthesized through spark plasma sintering (SPS). The composite exhibits excellent room temperature compressive properties with yield strength, ultimate strength and fracture strain of 1760 MPa, 2270 MPa and 11%, respectively. A model is presented to study the strengthening mechanism, and the theoretical calculation shows that the dramatically strength enhancement is mainly due to the in-situ formation of Ti-C-O particles.