Room Temperature Compression Research Articles

Processing and properties of low-temperature cure carbon fiber-reinforced bismaleimide composite

Bismaleimide (BMI) resins are used in carbon fiber reinforced composites for high-temperature applications. Conventional BMI resins require high cure and post-cure processing temperatures, which limit fabrication methods and contribute to residual stress and microcracking. Recently, BMIs with lower cure temperatures have been developed; however, little data on the properties of low-temperature cure carbon/BMI composites are available in the open literature. In this study, processing and properties of a low-temperature cure BMI resin system, referred to here as BMI-2, were evaluated. Along with evaluation of neat resin properties, multi-directional woven carbon fiber reinforced BMI-2 composite laminates were fabricated by an out-of-autoclave, vacuum-bag-only resin infusion method. New data on the mechanical, thermal, and moisture absorption properties are presented. It was found that the resin infusion method produced laminates with fiber volume fraction of approximately 55% and immeasurably low void content. BMI-2 was found to attain a degree of cure of 96% and glass transition temperature of 366°C following a 163°C cure cycle. Cured laminates did not suffer from process-induced cracking at the inter- or intra-laminar levels. Tensile strength and modulus of quasi-isotropic specimens with woven AS4 carbon fiber were 443 MPa and 47.6 GPa, respectively, and failure under quasi-static tension occurred by delamination. Compression strength was stable across a wide temperature range, with quasi-isotropic specimens retaining 60% of their room temperature compression strength at 260°C. Equilibrium moisture content of composite specimens was 1.2% by weight.

Effect of Ta and Ni on γ′ phase morphology and compression behavior of Co-8.8Al-9.8W superalloys

To investigate the effect of the γ′ phase morphology of cobalt-based superalloys on the plastic deformation behavior of the superalloys, Co-8.8Al-9.8W-2X (X=Ta, Ni) alloys were prepared to obtain superalloys with different morphologies of γ′ phases. The microstructure and room temperature compression behavior of superalloys were studied by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The results showed that the γ′ phase particles of 2Ta alloy are cubic, while that of 2Ni alloy is spherical. The compressive strength of 2Ta and 2Ni alloys are almost the same, but the hardness of 2Ta alloy is higher than that of 2Ni alloy, while the plastic deformability is significantly worse. 2Ta alloy exhibits quasi-cleavage fracture during compression, while 2Ni alloy showed a cleavage fracture, and amount of slip bands were found easily on the fracture surface of 2Ni alloy. The deformations of 2Ni alloy and 2Ta alloy were dominated by dislocations shearing γ′ phase particles. The γ′ phase of the 2Ni alloy underwent rafting, while that of 2Ta alloy did not change significantly.

Giant room temperature compression and bending in ferroelectric oxide pillars

Plastic deformation in ceramic materials is normally only observed in nanometre-sized samples. However, we have observed high levels of plasticity (>50% plastic strain) and excellent elasticity (6% elastic strain) in perovskite oxide Pb(In1/2Nb1/2)O3-Pb(Mg1/3Nb2/3)O3-PbTiO3, under compression along <100>pc pillars up to 2.1 μm in diameter. The extent of this deformation is much higher than has previously been reported for ceramic materials, and the sample size at which plasticity is observed is almost an order of magnitude larger. Bending tests also revealed over 8% flexural strain. Plastic deformation occurred by slip along {110} <1bar{1}0 > . Calculations indicate that the resulting strain gradients will give rise to giant flexoelectric polarization. First principles models predict that a high concentration of oxygen vacancies weaken the covalent/ionic bonds, giving rise to the unexpected plasticity. Mechanical testing on oxygen vacancies-rich Mn-doped Pb(In1/2Nb1/2)O3-Pb(Mg1/3Nb2/3)O3-PbTiO3 confirmed this prediction. These findings will facilitate the design of plastic ceramic materials and the development of flexoelectric-based nano-electromechanical systems.

In situ X-ray diffraction study on structural changes of neutron-irradiated highly oriented pyrolytic graphite under room-temperature compression and decompression

To clarify the nature of defects presented in neutron (n)-irradiated highly oriented pyrolytic graphite (HOPG), in situ X-ray diffraction (XRD) observation at room temperature (RT) and high pressure was conducted with synchrotron radiation (SPring-8). We focused on the graphite (002) [G(002)] peak under compression to 18.1 GPa and also under decompression. For comparison, unirradiated HOPG was also placed in the same high-pressure cell. We found that the G(002) peak can be represented by two components, the S and L peaks, for the n-irradiated HOPG, whereas it can be represented by only one component for the unirradiated HOPG. The d-spacing for the n-irradiated and unirradiated HOPG samples gradually decreased with increasing pressure. At 18.1 GPa, the d-spacing of the S peak of the irradiated sample became almost the same as that of the unirradiated one, but that of the L peak was larger. Under decompression, the behavior of the d-spacing was almost opposite to that under compression, and the d-spacing was restored to its value before compression. Also, taking account of the changes in the peak widths, we referred to and considered irradiation-induced defects of interstitial-type defects existing between the basal planes and in-plane defects of dislocation dipoles as possible defects that affect the changes in the G(002) peak.

The Grain Refinement and Deformation Mechanism of a Nano-Oxides Al2o3 Dispersion Strengthened Copper Alloy During Room Temperature Compression

The Grain Refinement and Deformation Mechanism of a Nano-Oxides Al2o3 Dispersion Strengthened Copper Alloy During Room Temperature Compression

Anisotropy of Mechanical Properties in Directionally Solidified Nb-Si Alloys at Room Temperature Compression

Anisotropy of Mechanical Properties in Directionally Solidified Nb-Si Alloys at Room Temperature Compression

Effect of compression loading speeds on the room temperature mechanical properties of as-extruded AZ31 magnesium alloy

The room temperature compression experiments of as-extruded AZ31 magnesium alloy under different loading speeds were carried out on a universal tensile testing machine. The fracture failure characteristics and mechanism of the alloy under different compression loading speeds were analyzed by scanning electron microscope (SEM) and optical microscope (OM). The results show that during the compression test, the crushed AZ31 magnesium alloy sample has a certain pier coarseness, the macro fracture of the sample is located at one third of the sample, and the macro fracture mode is 45° shear fracture with the sample axis; With the increase of loading speed, the coincidence degree of macro fracture becomes worse, and its compressive strength changes in an undulating manner. When the loading speed is 2mm/min, the compressive strength reaches the peak value of 413MPa, and the fracture morphology of the sample shows a typical flat and flat rock like ductile brittle mixed fracture. With the increase of loading speed, the proportion of brittle fracture components increases, the shape of shrinkage fracture is rock like fracture, and the fracture fluctuation is relatively slow, the dimples distributed on the fracture surface are elongated and torn, and the compression speed has no obvious effect on the fracture morphology.

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.

Twin evolution in cast Mg-Gd-Y alloys and its dependence on aging heat treatment

Effects of rare-earth (RE) and precipitates on twin evolution in cast Mg-10Gd-3Y-0.5Zr (wt.%) (GW103) alloys of solid solution (T4) and aged (T6) states are investigated performing quasi-static room temperature compression tests and microstructural characterization. It is found that both {10–12} and {11–21} extension twins (ET1 and ET2) can appear in the T4 and T6 states but with different emergence sequences. As the aging heat treatment leads to consumption of RE solutes which could inhibit atomic shuffling required for nucleation of ET1 but not ET2, ET2 occurs prior to ET1 in the T4 state, and ET1 emerges before ET2 in the T6 state. The extension twins here mainly coordinate the plastic deformation through the non-Schmid effect. Our results shed light on the influence of RE elements on twin evolution in magnesium alloys and have implications in developing high-performance Mg-RE alloys.

Effect of cryogenic cycling on mechanical properties of ZrTiCuNiBe bulk metallic glass

The effect of deep cryogenic cycle treatment (DCT) on Zr41.2Ti13.8Cu12.5Ni10Be22.5 (Vit-1) bulk metallic glass (BMG) prepared from high-purity raw materials was investigated. After DCT, no obvious rejuvenation of the samples was detected. With an increasing number of cryogenic cycles, the hardness of the samples first decreased and then increased, the room-temperature compression plasticity first increased and then generally remained unchanged, and the impact toughness underwent almost no obvious change. The absence of rejuvenation was attributed to the high fragility index (47–50) and high glass forming ability (GFA) of the material. As lower purity of the raw materials is expected in practical applications, DCT of Vit-1 BMG prepared from low-purity raw materials was also performed. After DCT, the samples prepared with the lower-purity raw materials were clearly rejuvenated, and the room-temperature mechanical properties improved significantly.Both the compression plasticity and impact toughness reached peak values after 5 cryogenic cycles. The initial impurities (including Y and O) had a complex and comprehensive effect on the deformation mechanism of the BMG during DCT. Our findings indicate that the structural heterogeneity, fragility index, and GFA of the BMG alter the effect of DCT.

Effect of Mg on dynamic recrystallization of Zn–Mg alloys during room-temperature compression

This work reveals the role of Mg additions on deformation behaviours of Zn–Mg alloys during room temperature compression at moderately high strain rate of ∼0.5 s-1. Experimental results from scanning electron microscopy, transmission electron microscopy and electron backscatter diffraction provide insight into the deformation behaviours and dynamic recrystallization mechanisms operative in Zn-0.08%Mg and Zn-0.8%Mg alloys. The primary dynamic recrystallization mechanisms in the Zn-0.08%Mg alloy were continuous dynamic recrystallization in conjunction with twin-induced dynamic recrystallization. After straining to a true strain of 161%, the Zn-0.08%Mg alloy displayed a uniform and heavily refined microstructure with an excellent combination of strength and plasticity. For the Zn-0.8%Mg alloy, particle-induced dynamic recrystallization activated by eutectic structures played a critical role in addition to continuous and twin-induced dynamic recrystallization mechanisms. Fine and soft-oriented grains which formed in proximity to the eutectic accommodated large amounts of localized plastic strain. This resulted in inhomogeneous strain partitioning which restricted dynamic recrystallization kinetics in hard-oriented grain interior regions due to insufficient slip activity to support continuous dynamic recrystallization. Therefore, a partially recrystallized microstructure was maintained in the Zn-0.8%Mg alloy up to true strain of 161%.

Processing of Ti/(HA+ZrO2) biocomposite and 50% porous hybrid scaffolds with low Young's modulus by powder metallurgy: Comparing of structural, mechanical, and corrosion properties

Processing of titanium (Ti)-based implants with improved corrosion resistance and Young’s modulus close to that of cortical bone are receiving considerable attention in orthopedic and dental applications. Therefore, Ti matrix, hydroxyapatite (HA) and hydroxyapatite-zirconia (HA+ZrO2) reinforced composites were successfully produced using powder metallurgy as both bulk and 50% in vol. porous scaffold in this study. Microstructure, mechanical and corrosion properties of the bulk and scaffold composites were investigated comparatively. Scanning electron microscopy with attached an energy dispersive spectroscopy (SEM-EDS) and XRD diffraction analysis was used for the characterization of samples. Mechanical properties were determined by using micro Vickers hardness and compressive tests. Besides, the corrosion behaviours of the samples were determined in simulated body fluid (SBF) at 37 °C by using potentiodynamic scanning (PDS) tests. Room-temperature compression tests revealed that the bulk samples had higher values of Young’s modulus and yield strength in comparison to the scaffold samples where the lowest values of Young’s modulus and yield strength of 3 GPa and 6.93 MPa, respectively were obtained in the case of the Ti/(HA+ZrO2) composite scaffold. Moreover, in-vitro corrosion tests in SBF showed that the Ti/(HA+ZrO2) composite scaffold had higher corrosion resistance than the scaffold reinforced with only the HA phase. The corrosion mechanism of the bulk and scaffold samples was also elucidated by taking the microstructural analysis and phase compositional of the samples into account.

Hot deformation behavior and microstructure evolution of NiAl-9HfO2 composite

The hot deformation behavior and microstructure evolution of the new NiAl-9%HfO2 composite synthesized by hot pressing sintering were researched by hot compression tests at temperatures of 1250–1400 °C and strain rates of 10−3-10−1 s−1 under a true strain of 0.693. The Arrhenius constitutive model was established on account of the stress-strain curves corrected by friction and adiabatic. The processing maps were also developed and the features of microstructure inferred by the processing map were corresponded to the microstructure observation. The optimum hot deformation processing window was 1300–1350 °C/0.03–0.01 s−1. In addition, the microstructure evolution and the softening mechanism during hot deformation were discussed in detail. Based on the room-temperature compression test, the samples deformed at 1350 °C with a strain rate of 0.03 s−1 exhibited the highest performance with the yield strength and ultimate compression deformation increasing by 22.6% and 52.2% compared with the original samples, respectively. This work provided more theoretical guidance for the hot processing of NiAl-based composites and further promoted their application.

Compression Behavior of Carbon‐Bonded Alumina Spaghetti Filters at Room and High Temperatures

The room and high temperature compression behavior of carbon‐bonded alumina spaghetti filters is investigated. The samples developed for high‐temperature steel melt filtration are produced by alginate‐based robo gel casting. In comparison with foam filters with hollow struts made by the replica technique, the spaghetti filters manufactured via the novel route exhibit full strut cross section. Brittle behavior of the samples is observed at room temperature and 800 °C, whereas at 1500 °C, the material shows ductile deformation. Moreover, the compressive strength at 1500 °C is higher than that at room temperature and 800 °C. In comparison with the previously studied carbon‐bonded alumina foam filters of similar bulk material composition and similar size produced by the replica method, the spaghetti filters exhibit significantly higher compression strength at high temperatures. The full struts and the relatively high bulk density of the spaghetti filters have positive influence on their mechanical strength.

A New Approach for Manufacturing Stochastic Pure Magnesium Foam by Laser Powder Bed Fusion: Fabrication, Geometrical Characteristics, and Compressive Mechanical Properties

Herein, stochastic pure magnesium foam using laser powder bed fusion (LPBF) is fabricated and its geometric characteristics and mechanical properties are investigated. As volumetric energy density (VED) increased from 20 to 40 J mm−3 by controlling process parameters, porosity changed to 42.7 and 40.5%, respectively. Furthermore, the average sizes of interior consolidated/pore areas were 154.6 μm/142.9 μm (20 J mm−3 VED) and 230.8 μm/182.2 μm (40 J mm−3 VED), respectively. Magnesium foam induces lack‐of‐fusion defects through variable control of the LPBF process, and as such defects are connected, open pore structures are suggested to be formed. Stochastic pure Mg foam is composed of a main α‐Mg phase and a small amount of MgO phases. Room temperature compression test results obtained compressive yield strengths of 37 MPa (20 J mm−3) and 46 MPa (40 J mm−3). Compared with conventional pure Mg foam with similar relative density, LPBF Mg foam had relatively greater mechanical properties. This is considered to be due to the fine twin‐like microstructure formed by rapid solidification during LPBF. In conclusion, with LPBF, a biocompatible Mg foam with an open pore structure and outstanding mechanical properties was manufactured efficiently.

Microstructure, distortion characteristics and mechanical behaviour of NiB modified 90W-6Ni-4Co heavy alloys

In this work, the effect of NiB on densification, phase, microstructure, distortion and mechanical properties of conventionally sintered ternary 90W-6Ni-4Co heavy alloy has been investigated without altering (Ni+NiB)/Co ratio. No intermetallic phase was detected in the heavy alloys upon addition of NiB. Instead, the partial and complete exchange of Ni with NiB in 90W-6Ni-4Co has elicited relatively better densification (>99% theoretical), higher bulk hardness (HV3 ~ 389–396 VHN), higher hardness of matrix (~352 HV0.025) when the alloys were sintered at 1500 °C. In addition to W grains and matrix, the completely NiB-substituted heavy alloy (90W-6NiB-4Co) sintered at 1500 °C exhibits the occurrence of W-rich third phase which contains ~75 wt% of W. Although the samples prevented slumping at 1475 °C, elephant foot formation was found inevitable in the base composition (90W-6Ni-4Co) when sintering was carried out at 1500 °C. However, the decreased distortion parameter (from 24.8 to 8.5) with optimal NiB addition affirms the enhanced shape retention capability of 90W-3Ni-3NiB-4Co and 90W-6NiB-4Co heavy alloys. Room temperature compression test of WHAs sintered at 1475 °C was performed at a fixed strain rate of 0.1 s-1. No crack formation was observed in NiB containing samples up to 40% deformation. Moreover, the systematic addition of 3–6 wt% NiB resulted in lower coefficient of thermal expansion of NiB-containing heavy alloys in the temperature range of 400–600 °C.

Microstructure stability during high temperature deformation of CoCrFeNiTa eutectic high entropy alloy through nano-scale precipitation

Dual-phase microstructures arising out of eutectic reactions offer several advantages: ease of casting, composite properties and tunable characteristic length scale of the phases. Eutectic high entropy alloys (EHEA) with a multi-component solution phase and a hard intermetallic phase are candidate materials to identify alternate high-temperature materials. Alloying elements can be chosen to improve the resistance to lamellar microstructure degradation and coarsening. In this work, we present the CALPHAD guided design of a hypo-eutectic high entropy alloy CoCrFeNiTa0.395 with primary dendritic FCC phase and fine eutectic (FCC solution + Laves phase) microstructure possessing good high-temperature mechanical properties. The primary FCC phase fraction is 0.42 ± 0.02. The interlamellar spacing of the eutectic is 0.69 ± 0.12 μm. The alloy exhibited a balanced yield strength of 1303 ± 18 MPa, a fracture strength of 2237 ± 23 MPa and a fracture strain of 0.3 under room temperature compression testing. The mechanism for change in the lamellar morphology during deformation at temperatures beyond 0.8 TE is explained schematically. Strain field distribution obtained by FEM simulation correlates well with the observed microstructure gradients in the deformed samples. The formation of nano-scale precipitates in the low strain rate deformation is attributed to thermal effects. High-temperature precipitation of two types of precipitates (L12 ordered and Ni3Ta type) in the FCC-solution phase extended the useable temperature range of this alloy.

Phase Stability of Iron Nitride Fe4N at High Pressure-Pressure-Dependent Evolution of Phase Equilibria in the Fe-N System.

Although the general instability of the iron nitride γ′-Fe4N with respect to other phases at high pressure is well established, the actual type of phase transitions and equilibrium conditions of their occurrence are, as of yet, poorly investigated. In the present study, samples of γ′-Fe4N and mixtures of α Fe and γ′-Fe4N powders have been heat-treated at temperatures between 250 and 1000 °C and pressures between 2 and 8 GPa in a multi-anvil press, in order to investigate phase equilibria involving the γ′ phase. Samples heat-treated at high-pressure conditions, were quenched, subsequently decompressed, and then analysed ex situ. Microstructure analysis is used to derive implications on the phase transformations during the heat treatments. Further, it is confirmed that the Fe–N phases in the target composition range are quenchable. Thus, phase proportions and chemical composition of the phases, determined from ex situ X-ray diffraction data, allowed conclusions about the phase equilibria at high-pressure conditions. Further, evidence for the low-temperature eutectoid decomposition is presented for the first time. From the observed equilibria, a P–T projection of the univariant equilibria in the Fe-rich portion of the Fe–N system is derived, which features a quadruple point at 5 GPa and 375 °C, above which γ′-Fe4N is thermodynamically unstable. The experimental work is supplemented by ab initio calculations in order to discuss the relative phase stability and energy landscape in the Fe–N system, from the ground state to conditions accessible in the multi-anvil experiments. It is concluded that γ′-Fe4N, which is unstable with respect to other phases at 0 K (at any pressure), has to be entropically stabilised in order to occur as stable phase in the system. In view of the frequently reported metastable retention of the γ′ phase during room temperature compression experiments, energetic and kinetic aspects of the polymorphic transition are discussed.

TRIP-assisted compressive ductility in Ti-rich Ti60Mo10V10Cr10Zr10 refractory medium-entropy alloy

Compositional tuned non-equiatomic refractory high-entropy alloys are coveted materials as they achieve considerable plasticity through transformation-induced plasticity (TRIP) behavior. In this study, a novel Ti-rich Ti60Mo10V10Cr10Zr10 refractory medium-entropy alloy (RMEA) was designed using FactSage. The plastic deformation of the alloy produced using vacuum arc remelting was investigated through a room-temperature compression test at different strain rates. A high strain-hardening rate and an m-value of 0.031 were observed in the Ti-rich Ti60Mo10V10Cr10Zr10 RMEA. The dimple structures formed in BCC phases and TRIP-assisted deformation attribute to the strength and ductility trade-off in Ti-rich Ti60Mo10V10Cr10Zr10 RMEA.

Microstructure evolution of as-extruded Zn–0.62Mn alloys during room temperature compression

The microstructure evolution of Zn–0.62Mn alloys during the room temperature compression with different strains was investigated by scanning electron microscope and X-ray diffraction. The results showed that with the increasing compression strains, the refined dynamic recrystallization grains increase gradually, and some grains rotate. It can also be found that the compression strain promotes the transformation from small-angle grain boundary to large-angle grain boundary. The highest basal textural can be obtained after the room-temperature compression with 80% strain. These results indicate that the microstructure evolution of as-extruded Zn–0.62Mn alloys during the room-temperature compression can be attributed to the grain refinement, grain boundary variation and texture changes.