Good Compressive Ductility Research Articles

A multi-principal element alloy combining high specific strength and good ductility

• Al8Nb27Ti29V28Zr8 multi-principal element alloy prepared by arc melting. • Alloy composed of an A2 disordered BCC structure and nanometer-sized particles. • The density is 6.34 g cm −3 . • High specific strength and good compression ductility at room temperature. • High specific strength at temperatures near 700 °C. Al 8 Nb 27 Ti 29 V 28 Zr 8 multi-principal element alloy (MPEA) was prepared via arc melting. In the homogenized + heat treated condition the alloy is composed essentially of a matrix possessing A2 disordered BCC structure and nanometer-sized particles of Al 3 Zr 5 and Laves AlZrV phases. The alloy demonstrated high yield strength (1250 MPa) and good compressive ductility (38 % until fracture) at room temperature, and maintained a high yield strength at 700 °C (720 MPa). The density was measured as 6.34 g.cm −3 , resulting in a specific strength at 700 °C of 113.6 kPa.m 3 /kg, near twice that of Ti6Al4V (67.7 kPa.m 3 /kg) and Inconel 625 (46.2 kPa.m 3 /kg) alloys, and more than three times higher than that of Ti-β21S (35.4 kPa.m 3 /kg). However, the tests performed and results obtained were not sufficient to explain the simultaneous high yield stress and ductility at room temperature.

Investigations on microstructure and properties of Ti-Nb-Zr medium-entropy alloys for metallic biomaterials

In this study, three medium entropy alloys (MEAs), TiNbZr, Ti1.5Nb1.5Zr and Ti1.5NbZr1.5 were designed and investigated to be applied as biomedical materials. The results showed that the alloys prepared by arc melting have a typical dendrite microstructure, caused by elemental segregation during solidification. With composition changes, the partition of the constituting elements behaves differently. The microstructure inhomogeneity and chemical segregation could be greatly reduced by homogenization treatment. The MEAs show good compressive ductility (>40%) and yield strength comparable to or even superior to those of the commercially used biomedical alloys (e.g., 316 stainless steel and pure titanium), which are mainly contributed from the solid-solution strengthening effect. In addition, these MEAs exhibit acceptable Young's modulus ranging from 80 to 93 GPa by nano-indentation tests. The alloys also show excellent corrosion resistance in the phosphate buffer saline (PBS) solution and favorable cyto-compatibility, which are comparable to or even superior to pure titanium and/or Ti-6Al-4V alloys. Based on these properties, the Ti-Nb-Zr MEAs show a promising potential in biomedical applications. The results in this study could be instructive for further alloy design of such biomedical MEAs.

Effects of Si additions on microstructures and mechanical properties of VNbTiTaSix refractory high-entropy alloys

(VNbTiTa)100-xSix (x = 0, 2.5, 5, 10) refractory high-entropy alloys (RHEAs) are investigated in this paper. The equal molar VNbTiTa RHEA exhibits a room-temperature yield strength of 704 MPa and good compressive ductility (fracture strain> 50%). Si additions can introduce BCC+M5Si3 eutectic formed at inter-dendrite areas, and when the Si content reaches 10% in mole, extra bulk M3Si phase was observed. The precipitated silicides greatly improve the yield strength up to 1671 MPa. As the temperature increases, the strengthening effect of silicide becomes weaker, and almost disappeared at 1200 ℃. Nanoscale silicides can precipitate during high-temperature deformations. (VNbTiTa)97.5Si2.5 RHEA possesses an excellent combination of room-temperature ductility 34% and yield strength 505 MPa at 1000 ℃.

The role of incoherent interface in evading strength-ductility trade-off dilemma of Ti2AlN/TiAl composite: A combined in-situ TEM and atomistic simulations

The strength-ductility trade-off dilemma has inhibited the applications of many structural materials, TiAl alloys in particular. Here we report a new insight into the potential for increasing the ductility of Ti2AlN/TiAl composite without lowering its strength by tuning the interface with a unique incoherent atomic structure. The in-situ TEM nanoindentation tests indicate that the Ti2AlN(101‾3)//TiAl(111) incoherent interface micro-region possesses high compressive strength and good compressive ductility, because this incoherent interface can simultaneously play the role of softening and hardening in the process of compression due to the interface-dominated nucleation and annihilation of dislocations. The first-principles calculation and MD simulation results reveal that the reason why this incoherent interface displays a distinct compressive deformation behavior is that it has unique atomic structure, bonding character and interface-dislocation interactive mechanisms. By using first-principles calculations, it is found that this incoherent interface possesses a hierarchical atomic structure in the direction normal to the interface, the interface bonding characteristics are multiple and inhomogeneous depending on local atomic configurations, forming both the strong and weak interface interactive regions. The MD simulations indicate that the weakest interface interactive regions, i.e. incoherent regions in the Al2 atomic arrays of Ti2AlN(101‾3) plane at the interface, could provide the preferred nucleation source for primary dislocations, incepting the plastic deformation. After the deformation achieves a certain extent, the local disordered interface regions generated by internal stress shearing could act as sinks to annihilating the secondary dislocations propagated from Al1 atomic layer of Ti2AlN(0001) plane, resulting in strain hardening.

High‐Entropy Alloy (HEA)‐Coated Nanolattice Structures and Their Mechanical Properties

Nanolattice structure fabricated by two‐photon lithography (TPL) is a coupling of size‐dependent mechanical properties at micro/nano‐scale with structural geometry responses in wide applications of scalable micro/nano‐manufacturing. In this work, three‐dimensional (3D) polymeric nanolattices are initially fabricated using TPL, then conformably coated with an 80 nm thick high‐entropy alloy (HEA) thin film (CoCrFeNiAl0.3) via physical vapor deposition (PVD). 3D atomic‐probe tomography (APT) reveals the homogeneous element distribution in the synthesized HEA film deposited on the substrate. Mechanical properties of the obtained composite architectures are investigated via in situ scanning electron microscope (SEM) compression test, as well as finite element method (FEM) at the relevant length scales. The presented HEA‐coated nanolattice encouragingly not only exhibits superior compressive specific strength of ≈0.032 MPa kg−1 m3 with density well below 1000 kg m−3, but also shows good compression ductility due to its composite nature. This concept of combining HEA with polymer lattice structures demonstrates the potential of fabricating novel architected metamaterials with tunable mechanical properties.

Mechanical properties of low-density, refractory multi-principal element alloys of the Cr–Nb–Ti–V–Zr system

Room temperature and elevated temperature mechanical properties of four multi-principal element alloys, NbTiVZr, NbTiV2Zr, CrNbTiZr and CrNbTiVZr, are reported. The alloys were prepared by vacuum arc melting followed by hot isostatic pressing and homogenization. Disordered BCC solid solution phases are the major phases in these alloys. The Cr-containing alloys additionally contain an ordered FCC Laves phase. The NbTiVZr and NbTiV2Zr alloys showed good compressive ductility at all studied temperatures while the Cr-containing alloys showed brittle-to-ductile transition occurring somewhere between 298 and 873K. Strong work hardening was observed in the NbTiVZr and NbTiV2Zr alloys during deformation at room temperature. The alloys had yield strengths of 1105MPa and 918MPa, respectively, and their strength continuously increased, exceeding 2000MPa after ∼40% compression strain. The CrNbTiZr and CrNbTiVZr alloys showed high yield strength (1260MPa and 1298MPa, respectively) but low ductility (6% and 3% compression strain) at room temperature. Strain softening and steady state flow were typical during compression deformation of these alloys at temperatures above 873K. In these conditions, the alloys survived 50% compression strain without fracture and their yield strength continuously decreased with an increase in temperature. During deformation at 1273K, the NbTiVZr, NbTiV2Zr, CrNbTIZr, and CrNbTiVZr alloys showed yield strengths of 58MPa, 72MPa, 115MPa and 259MPa, respectively.

Bulk gold with hierarchical macro-, micro- and nano-porosity

Millimeter-sized, free-standing gold structures were created with three levels of multiscale porosity. First, macro- and microporosity, which are useful for mass and heat transport within the structure, are formed within an Ag–19at.% Au alloy by salt powder replication during powder densification and by entrapped gas expansion during sintering, respectively. Nanoporosity, which provides high surface area, is then produced by silver dealloying of these Ag–19at.% Au foams. The resulting hierarchical gold structures are annealed at 100–800°C, thus coarsening the ligaments, increasing relative density, and healing cracks produced during dealloying. The first effect weakens the structure, while the other two make it stronger. A bulk Au sample with hierarchical porosity annealed at 600°C shows good compressive ductility and a strength in agreement with models.

Structure and mechanical properties of Ti–6Al–4V with a replicated network of elongated pores

Ti–6Al–4V, with a network of elongated, open pores aligned along two perpendicular directions, is produced by a two-step replication process: (i) Ti–6Al–4V powder or foil preforms containing low-carbon steel wire meshes are densified by hot pressing under transformation superplasticity conditions; (ii) porosity is created by electrochemical dissolution of the low-carbon steel wires and the adjacent Fe-containing Ti–6Al–4V matrix. If high-carbon steel wires are used, Fe diffusion into Ti–6Al–4V is inhibited by a carbide layer forming at the wire/matrix interface, and pores exactly replicate the shape of the wires. Ti–6Al–4V with ∼19% and 34% porosity, without and with Fe–Ti interdiffusion respectively, shows low oxygen contamination and good compressive ductility. Strength and stiffness, as measured by compression testing and ultrasonic measurements, are compared with simple analytical models and numerical finite-element models.

The role of Hf and TiC additions in the mechanical properties and microstructure of NbAlV alloys

The microstructures and mechanical properties of Nb–12Al–20V (at.%) containing Hf or TiC have been investigated. The microstructures were characterised using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The NbAlV alloy is single B2 phase, the 5% Hf added completely dissolving into the matrix. The addition of 5% Hf and 5% TiC resulted in the formation of MC-type Hf-rich carbide. Compression testing has been carried out at room temperature, 1273 and 1473 K. The alloys show good compression ductility at room temperature. Hf addition gave a slight increase in strength at both room temperature and high temperature. The addition of both Hf and TiC significantly improves the strength. The room temperature strength of these alloys could be well described by solid solution strengthening and a load transfer mechanism. The alloys deform primarily via dislocation slip, with some mechanical twinning.

Effect of carbon on the microstructures and mechanical properties of as cast Nb-base alloy

Microstructure and mechanical properties of Nb35Ti6Al5Cr8V (at.%) containing different C contents (0, 1, 11.6 at.%) were investigated. The microstructures were characterized using optical microscopy and scanning and transmission electron microscopy (SEM and TEM, respectively). The alloy without C appeared single phase: Nb solid solution (Nbss). The carbide in 1% C alloy is fcc MC. The addition of 11.6% C resulted in the formation of two types of particles: primary carbide ((Ti,Nb) 2C) and secondary carbide ((Ti,Nb)C). Compression testing was carried out at room temperature, 1073, 1273 and 1473 K. The alloys showed good compression ductility at room temperature. The strengths at room and high temperature increase with increasing C content, but the room temperature ductility decreases.

Ultrahigh strength binary Ni–Nb bulk glassy alloy composite with good ductility

Materials may be strong or ductile, but rarely both at once. However, the combination of high strength and good ductility is significant for application of materials as structural materials. In this work, we report a Ni–Nb alloy, which exhibits ultrahigh compressive strength of up to 3500 MPa together with good compressive ductility of 5.3%. To the best of our knowledge, the plastic strain is larger than previous values reported for any bulk ultrahigh strength (over 3000 MPa) alloys. The good ductility is due to the heterogeneous microstructure of the alloy.

Effect of Mo and Hf on the mechanical properties and microstructure of Nb–Ti–C alloys

The microstructures and mechanical properties of Nb–20Ti–12.5C (at.%) containing different Mo or Hf contents have been investigated. The microstructures were characterized using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The alloy without Mo and Hf contains Nb solid solution (Nbss), (Ti,Nb) 2C/Nbss eutectic, primary (Ti,Nb) 2C and secondary (Ti,Nb)C. The addition of Mo or Hf restrains the precipitation of (Ti,Nb)C. No Mo-rich precipitates were observed. Part of the Hf appeared as (Hf,Ti,Nb) 2C-type carbide. Compression testing has been carried out at room temperature and 1473 K. The alloys showed good compression ductility at room temperature and Nb20Ti12.5C20Mo produced a 0.2% offset yield stress of 300 MPa at 1473 K. The room temperature and high temperature strengths increase with increasing Mo, but the room temperature ductility decreases. Hf additions however did not much change the strength because half the Hf dissolved in the carbides and there was not much modification of their volume fraction.

Ultrafine-grained Al–Al2Cu composite produced in situ by friction stir processing

Ultrafine-grained Al–Al2Cu composite can be fabricated in situ by friction stir processing. The Al2Cu particles are distributed quite homogeneously in the composite. The composite possesses enhanced Youngs modulus, good compressive strength and reasonably good compressive ductility.

Compressive mechanical properties of multi-phase alloys based on B2 CoAl and E2 1 Co 3AlC

Mechanical behavior of multi-phase alloys, consisting of intermetallic compounds B2 type CoAl and E2 1 type Co 3AlC with primary solid solution (Co), was investigated by compression tests over a wide temperature range from 77 to 1273 K. It has been revealed that E2 1 Co 3AlC is a good candidate of coexisting phase with B2 CoAl to improve the alloy's ambient temperature ductility and its elevated temperature strength. Most of the multi-phase Co–Al–C ternary alloys exhibit fairly good compressive ductility at whole test temperatures, even at 77 K. All the alloys show the anomalous positive temperature dependence of strength at intermediate temperatures. The deformation mechanism of E2 1 Co 3AlC is expected to be the same as that of L1 2 intermetallic compounds because of the close resemblance of their crystal structures. The three-phase B2/E2 1/(Co) alloy, 70Co20Al10C(at%), exhibits excellent ductility of virtually unlimited ambient temperature compressive plastic strain and the highest strength around 340 MPa at 1273 K.

Dissociation of glide dislocations and apb energy in L12(Al,Cr)3Ti alloys

The L1[sub 2] trialuminides with a cubic structure are receiving much attention because of the importance as potential high temperature structural materials. These alloys contain a high amount of alumium and thus have an advantage of good economy. Among them, chromium-modified (Al,Cr,)[sub 3]Ti has been reported to have high resistance to high temperature oxidation, as well as ambient compressive ductility. The alloys show good compressive ductility even at room temperature, but only a fraction of per cent of tensile elongation has been reported. However, no clear explanation has been made for the origin of this rather peculiar behavior of the alloys. Moreover, it is still in question as to whether or not the observed ductility behavior comes from the intrinsic nature of the alloys. In the present investigation, observation by TEM was made of dislocation structures in chromium-modified alloys induced by compressive deformation. Focus was on the dissociation mode of glide dislocations and also on the energy of the planar defect in connection with possible ductility of the alloys.

The Role of Dispersoids in Mechanically Alloyed NiAl

Mechanical alloying followed by hot extrusion has been used to produce fully dense, crack free, very fine grained NiAl-based alloys containing a bimodal distribution of aluminum oxide dispersoids. The unique microstructure provides the materials with high strength and good compressive ductility at ambient and elevated temperatures. The emphasis of the paper is on the importance of the dispersion phase in controlling grain size, texture, deformation mechanisms and ultimately mechanical properties of the mechanically alloyed NiAl-based materials.

Plastic deformation of the intermetallic compound Al3Ti

Abstract Polycrystalline specimens of the intermetallic compound Al3Ti with the D022-type structure have been deformed under compression at 25–860°C. At temperatures below 620°C, specimens fracture with very small fracture strain since extremely localized deformation occurs and cracks are initiated in intensely deformed regions almost at yielding. At temperatures above 620°C, good compression ductility is observed. Yield stress starts decreasing rapidly with increasing temperature at around 330°C and becomes less temperature dependent above 630°C. The major mode of deformation of Al3Ti is twinning of the type (111)[112] which does not disturb the D022 symmetry of the lattice. However, at high temperatures, the four (111)[112]-type twinning systems are augmented by slip of the types [110], [100] and [010]. This would supply an explanation for the good compression ductility observed at temperatures above 620°C. Suggestions are made for further experimental work on alloying additions which may improve the du...

Mechanical prperties and microstructure of heat-treated ultrahigh carbon steels

The mechanical properties of submicron grain size plain carbon steels (1.3 and 1.6% C) have been studied after heat treatment. It has been shown that such steels can be austenitized and quenched to high hardness ( R c = 67), high compression fracture strength (4345 MPa (about 630 klbf in −2)), and good compression ductility (about 10%). These unusual and desirable characteristics are achieved by austenitizing at low temperature, where a fine austenite grain size exists, prior to quenching. In contrast, austenitizing at high temperature leads to a decrease in fracture strength because of a coarsening of the transformation products. Microscopic studies of samples quenched from low austenitizing temperatures revealed the presence of optically unresolvable martensite and fine undissolved cementite. Transmission electron microscope studies showed a structure consisting mostly of submicron lath martensite, some very fine twin martensite regions and undissolved cementite particles.