Microstructure and mechanical properties of nano-Y2O3 dispersed ferritic steel synthesized by mechanical alloying and consolidated by pulse plasma sintering

Ferritic steel with compositions 83.0Fe–13.5Cr–2.0Al–0.5Ti (alloy A), 79.0Fe–17.5Cr–2.0Al–0.5Ti (alloy B), 75.0Fe–21.5Cr–2.0Al–0.5Ti (alloy C) and 71.0Fe–25.5Cr–2.0Al–0.5Ti (alloy D) (all in wt%) each with a 1.0?wt% nano-Y₂O₃ dispersion were synthesized by mechanical alloying and consolidated by pulse plasma sintering at 600, 800 and 1000°C using a 75-MPa uniaxial pressure applied for 5?min and a 70-kA pulse current at 3?Hz pulse frequency. X-ray diffraction, scanning and transmission electron microscopy and energy disperse spectroscopy techniques have been used to characterize the microstructural and phase evolution of all the alloys at different stages of mechano-chemical synthesis and consolidation. Mechanical properties in terms of hardness, compressive strength, yield strength and Young's modulus were determined using a micro/nano-indenter and universal testing machine. All ferritic alloys recorded very high levels of compressive strength (850–2850?MPa), yield strength (500–1556?MPa), Young's modulus (175–250?GPa) and nanoindentation hardness (9.5–15.5?GPa), with up to 1–1.5 times greater strength than other oxide dispersion-strengthened ferritic steels (<1200?MPa). These extraordinary levels of mechanical properties can be attributed to the typical microstructure of uniform dispersion of 10–20-nm Y₂Ti₂O₇ or Y₂O₃ particles in a high-alloy ferritic matrix.     

Effects of Nb Additions and Heat Treatments on the Microstructure,Hardness and Wear Resistance of CuNiCrSiCoTiNbx High-Entropy Alloys

In this research, a set of CuNiCrSiCoTi (H-0Nb), CuNiCrSiCoTiNb_0.5 (H-0.5Nb) and CuNiCrSiCoTiNb₁ (H-1Nb) high-entropy alloys (HEAs) were melted in a vacuum induction furnace. The effects of Nb additions on the microstructure, hardness, and wear behavior of these HEAs (compared with a CuBe commercial alloy) in the as-cast (AC) condition, and after solution (SHT) and aging (AT) heat treatments, were investigated using X-ray diffraction, optical microscopy, and electron microscopy. A ball-on-disc configuration tribometer was used to study wear behavior. XRD and SEM results showed that an increase in Nb additions and modification by heat treatment (HT) favored the formation of BCC and FCC crystal structures (CS), dendritic regions, and the precipitation of phases that promoted microstructure refinement during solidification. Increases in hardness of HEA systems were recorded after heat treatment and Nb additions. Maximum hardness values were recorded for the H-1Nb alloy with measured increases from 107.53 HRB (AC) to 112.98 HRB, and from 1104 HV to 1230 HV (aged for 60 min). However, the increase in hardness caused by Nb additions did not contribute to wear resistance response. This can be attributed to a high distribution of precipitated phases rich in high-hardness NiSiTi and CrSi. Finally, the H-0Nb alloy exhibited the best wear resistance behavior in the aged condition of 30 min, with a material loss of 0.92 mm³.     

AlCrFeCuNi高熵合金力学性能的分子动力学模拟

高熵合金具有传统合金无法比拟的高强度、高硬度和高耐磨耐腐蚀性,具有广阔的应用前景。为研究AlCrFeCuNi高熵合金(High entropy alloy,HEA)在轴向载荷作用下的力学性能,采用分子动力学方法,模拟高熵合金的实验制备过程并建立原子模型,研究温度和Al的含量对AlCrFeCuNi高熵合金力学性能的影响,从材料学角度分析了变形过程及其具有高塑性的原因。模拟结果表明,AlCrFeCuNi高熵合金在拉伸载荷作用下依次经历弹性、屈服、塑性3个变形阶段。在屈服阶段,开始出现孪晶和层错,孪晶和层错的产生和生长是合金产生不均匀塑性变形的主要原因之一。高熵合金的杨氏模量和屈服应力随着Al含量的增加近似线性降低,同时具有很强的温度效应,温度越低,Al含量越小,其杨氏模量和屈服应力的下降幅度越大。     

Concentration-dependent crystal structure,elastic constants and electronic structure of Zr x Ti1−x alloys under high pressure

The physical properties of ZrxTi1-x（x=0.0, 0.33, 0.5, 0.67, 0.75 and 1.00） alloys were sinmlated by virtual crystal approximation （VCA） methods which is generally used for disordered solid solutions modeling. The elastic constant, electronic structure and thermal Equation of state （EOS） of disor- dered ZrxTi1-x alloys under pressure are investigated by plane-wave pseudo-potentia1 method. Our simulations reveal increasement of variations of the calculated equilibrium volumes and decrease- ment of Bulk modulus as a function of the alloy compositions. Lattice parameters a and c of alloys with differentZr concentrations decrease linearly with pressure increasing, but the c/avalues are increasing as pressure increases, indicating no phase transitions under pressure from 0 GPa to 100 GPa. The elastic constants and the Bulk modulus to the Shear modulus ratios （B/G） indicate good ductility of Zr, Zr0.33 Ti0.67 Zr0.5Ti0.5, Zr0.75Ti0.25 and Ti, but the Zr0.67Ti0.33 alloy is brittle under 0 K and 0 GPa. The metallic behavior of these alloys was also proved by analyzing partial and total DOS.     

A New Cu-Based Metallic Glass Composite with Excellent Mechanical Properties

A new Cu-based bulk metallic glass composite of nominal composition(at.%) Cu_(41)Ni_(27)Ti_(25)Al_7 with excellent plasticity and a strong work-hardening behavior is fabricated. Strength above 1859 MPa and plasticity more than 11% are achieved under compression and tension modes. The deformation mechanism is proposed to the structural heterogeneities of the composite that promotes multiple shear bands meanwhile inhibits their free propagation,which results in the macroscopically plastic strain and work hardening. The alloy contains relatively cheap metals and has a low cost, which is beneficial to industrial applications.     

New class of plastic bulk metallic glass

An intrinsic plastic Cu(45)Zr(46)Al(7)Ti(2) bulk metallic glass (BMG) with high strength and superior compressive plastic strain of up to 32.5% was successfully fabricated by copper mold casting. The superior compressive plastic strain was attributed to a large amount of randomly distributed free volume induced by Ti minor alloying, which results in extensive shear band formation, branching, interaction and self-healing of minor cracks. The mechanism of plasticity presented here suggests that the creation of a large amount of free volume in BMGs by minor alloying or other methods might be a promising new way to enhance the plasticity of BMGs.     

Effect of Ti on the Structure and Mechanical Properties of TixZr2.5-xTa Alloys

To determine the effects of Ti and mixing entropy (ΔS_mix) on the structure and mechanical proper-ties of Zr-Ta alloys and then find a new potential energetic structural material with good me-chanical properties and more reactive elements, Ti_xZr_2.5−xTa (x = 0, 0.5, 1.0, 1.5, 2.0) alloys were investigated. The XRD experimental results showed that the phase transformation of Ti_xZr_2.5−xTa nonequal-ratio ternary alloys depended not on the value of ΔS_mix, but on the amount of Ti atoms. With the addition of Ti, the content of the HCP phase decreased gradually. SEM analyses revealed that dendrite morphology and component segregation increasingly developed and then weakened gradually. When x increases to 2.0, Ti_xZr_2.5−xTa with the best mechanical properties can be ob-tained. The yield strength, compressive strength and fracture strain of Ti_2.0Zr_0.5Ta reached 883 MPa, 1568 MPa and 34.58%, respectively. The dependence of the phase transformation and me-chanical properties confirms that improving the properties of Zr-Ta alloys by doping Ti is feasible.     

Amorphous phase formation rules in high-entropy alloys

There have been many interesting studies on high-entropy alloys(HEAs), also known as multi-component(MC) alloys(MCAs), in recent years. MC metallic-glasses(MGs) have shown the potential to express the advantages of MCAs and MGs in tandem. Amorphous phase formation rules are a crucial issue in the HEA and MCA field. For equal or near-equal atomic ratio alloys, mixed-entropy among the elements has a significant effect on the phase formation. This paper focuses on HEA amorphous phase formation rules. In the first two sections, the recent progress in amorphous phase formation in HEAs and MCAs is reviewed, including the effective factors and correlative parameters related to amorphous phase formation. In the third section, novel MCMGs including high-entropy(HE) bulk-metallic-glass(HE-BMG) and MCMG films developed in recent decades are summarized, and the giant-magnetic-impedance(GMI) effect of MC amorphous fibers is discussed.     

Ductile Bulk Aluminum-Based Alloy with Good Glass-Forming Ability and High Strength

Based on a new approach for designing glassy alloy compositions, bulk Al-based alloys with good glass-forming ability （GFA） are synthesized. The cast Al86Si0.5Ni4.06Co2.94 Y6Sc0.5 rod with a diameter of i mm shows almost fully amorphous structure besides about 5% fcc-Al nucleated in the center of the rod. The bulk alloy with high Al concentration exhibits an ultrahigh yield strength of 1.18 GPa and maximum strength of 1.27 GPa as well as an obvious plastic strain of about 2.4% during compressive deformation. This light Al-based alloy with good GFA and mechanical properties is promising as a new high specific strength material with good deformability.     

第一性原理计算Al元素含量对高熵合金AlxCoCrCuFeNi的影响

采用第一性原理密度泛函理论,结合平面波赝贽和广义梯度近似(GGA),用虚拟晶体近似(VCA)方法建模,计算了高熵合金Alx CoCrCuFeNi的结构性能、弹性性能及生成热.计算结果表明,高熵合金Alx CoCrCuFeNi的密度随Al元素摩尔含量的增大而减小,晶格常数在Al元素摩尔含量为1时最小.Al元素摩尔含量为2时,高熵合金Alx CoCrCuFeNi符合力学稳定性判据.生成热随Al元素摩尔含量增大而增大,皆为负值的生成热表明高熵合金在热力学条件下稳定.     

High-throughput screening for biomedical applications in a Ti-Zr-Nb alloy system through masking co-sputtering

A method of co-sputtering deposition combined with physical masking was applied to the parallel preparation of a ternary Ti-NbZr system alloy. Sixteen independent specimens with varying compositions were obtained. Their microstructure, phase structure,Young's modulus, nanoindentation hardness, and electrochemical behavior in a phosphate buffer solution(PBS) were studied in detail. It was revealed that the Ti-Zr-Nb alloys possess a single BCC structure. As confirmed via nanoindentation tests, the Young's modulus of the specimens ranged from 80.3 to 94.8 GPa and the nanoindentation hardness ranged from 3.6 to 5.0 GPa.By optimizing the composition of the specimens, the Ti_(34)Zr_(52)Nb_(14) alloy was made to possess the lowest modulus in this work(76.5 GPa). Moreover, the Ti_(34)Zr_(52)Nb_(14) alloy showed excellent corrosion resistance in PBS without any tendency for pitting at anodic potentials up to 1 Vsce. These preliminary advantages offer the opportunity to explore new orthopedic implant alloys based on Ti-Zr-Nb alloys. Moreover, this work provides an effective method for the parallel preparation of biomedical alloys.     

Structural and electronic properties of GaN x As1−x alloys

The structural and electronic properties of cubic GaN _x As_1−x with N-concentration varying between 0.0 and 1.0 with step of 0.25 were investigated using the full potential–linearized augmented plane wave (FP-LAPW) method. We have used the local density approximation (LDA) and the generalized gradient approximation (GGA) for the exchange and correlation potential. In addition the Engel-Vosko generalized gradient approximation (EVGGA) was used for the band-structure calculations. The structural properties of the binary and ternary alloys were investigated. The electronic band structure, total and partial density of states as well as the electron charge density were determined for both the binary and their related ternary alloys. The energy gap of the alloys decreases when we move from x=0.0 to 0.25; then it increases by a factor of about 1.8 when we move from 0.25 to 0.5, 0.75 and 1.0 using EVGGA. For both LDA and GGA moving from x=0.0 to 0.25 causes the band gap to close, showing the metallic nature of the GaN_0.25As_0.75 alloy. When the composition of N moves through x=0.25, 0.5, 0.75 and 1, the band gap increases.     

Effect of irradiation on microstructure and hardening of Cr–Fe–Ni–Mn high-entropy alloy and its strengthened version

ABSTRACT

A single-phase fcc high-entropy alloy (HEA) of 20%Cr–40%Fe–20%Mn–20%Ni composition and its strength with yttrium and zirconium oxides version was irradiated with 1.4?MeV Ar ions at room temperature and mid-range doses from 0.1 to 10 displacements per atom (dpa). Transmission electron microscopy (TEM), scanning transmission electron microscopy with energy dispersive X-ray spectrometry (STEM/EDS) and X-ray diffraction (XRD) were used to characterise the radiation defects and microstructural changes. Nanoindentation was used to measure the ion irradiation effect on hardening. In order to understand the irradiation effects in HEAs and to demonstrate their potential advantages, a comparison was performed with hardening behaviour of 316 austenitic stainless steel irradiated under an identical condition. It was shown that hardness increases with irradiation dose for all the materials studied, but this increase is lower in high-entropy alloys than in stainless steel.     

碳化钨对激光熔覆高熵合金的影响

为了获得高性能的涂层材料,采用激光熔覆的方法,在Q235钢基体上制备了FeSiCrCoMo高熵合金涂层,并研究了WC对高熵合金涂层的组织和性能的影响。通过金相、X射线衍射、扫描电镜、硬度计、磨损试验机分别研究了添加WC前后涂层的微观形貌、相结构、硬度及磨损性能。结果表明:高熵合金FeSiCrCoMo涂层组织为粗大枝状晶,主要由BCC相和金属间化合物构成,添加WC后,涂层中形成了致密细小的胞状晶,同时BCC相增多,金属间化合物明显减少;添加WC后涂层的硬度明显增强,平均硬度提升了23%,涂层表面平均硬度达到了687HV0.2;WC的添加使得涂层的摩擦系数减小,磨损率减小,耐磨性能提高。     

Effects and mechanism of ultrasonic irradiation on solidification microstructure and mechanical properties of binary TiAl alloys

In spite of their high temperature and reactivity, the binary TiAl alloys are successfully imposed by the ultrasonic irradiation and the microstructure evolution, solidification behaviors and mechanical properties are elaborately investigated. After ultrasonic irradiation, a high quality ingot without shrinkage defects and element segregation is obtained and the coarse dendrite structure is well modified into fine non-dendrite globular grains. The coarse lamellar colony and lamellar space of Ti44Al alloy is refined from 685 μm to 52 μm and 1185 nm to 312 nm, respectively (similarly, 819 μm to 102 μm and 2085 nm to 565 nm for Ti48Al alloy). For Ti48Al alloy, the α peritectic phase is simultaneously precipitated from the melt as well as the β primary phase before the peritectic reaction and the solidification is transformed into the mixed α-solidifying and β-solidifying. Ultrasonic irradiation promotes the peritectic reaction and phase transformation completely and the phase constituent becomes more close to the equilibrium level. The compressive strength of Ti44Al and Ti48Al alloys are increased from 623 MPa to 1250 MPa and 980 MPa to 1295 MPa, respectively. The grain refinement and dendrite transformation enhance the grain boundary sliding improving the plastic deformation ability. Ultrasonic irradiation significantly accelerates the melt flow and solute redistribution and the main grain refinement mechanism is the cavitation-enhanced nucleation by inclusion activation and heightened supercooling.     

3D打印激光制备多孔镍合金组织和力学性能研究

采用3D打印激光熔化技术制备了多孔镍基合金,并对其显微组织构成和压缩力学性能进行了分析。研究结果表明,采用3D打印激光熔化技术制备的多孔镍合金,孔隙率为14.68%~18.97%、抗压强度为461~535 MPa,其微观组织主要呈现γ-Ni枝晶,压缩断口为撕裂式枝晶断裂。     

Mg-Al系工业合金牌号的成分式解析

Mg-Al系牌号是应用最广的镁基工业合金,但其牌号背后的成分根源一直未知,构成研发新合金的主要障碍.本文应用描述固溶体短程序结构特征的团簇共振模型,得到了Mg-Al二元固溶体的最理想化学结构单元[Al-Mg_(12)]Mg_1,然后对《the American Society for Testing Materials》手册中所有Mg-Al系工业合金牌号进行成分解析,得到相应团簇成分式,如AZ63A合金解析后的团簇成分式为[Al_(0.78)Zn_(0.16)-Mg_(12)]Mg_(1.04)Mn_(0.02),AZ81A合金解析后的团簇成分式为[Al_(0.97)Zn_(0.03)-Mg_(12)]Mg_(0.98)Mn_(0.02).再根据成分式与化学结构单元之间的误差,对比该牌号合金的力学性能,验证了该化学结构单元在Mg-Al体系中的准确性,揭示出看似复杂的工业合金牌号后面隐藏的简单成分规律,为发展Mg-Al体系合金指出了一个全新的途径.     

Yttria catalyzed microstructural modifications in oxide dispersion strengthened V–4Cr–4Ti alloys synthesized by field assisted sintering technique

Abstract

The present work deals with synthesis, characterisation and elevated temperature mechanical property evaluation of V–4Cr–4Ti and oxide (yttria = 0.3, 0.6 and 0.9 at%) dispersion strengthened V–4Cr–4Ti alloy processed by mechanical alloying and field-assisted sintering, under optimal conditions. Microstructural parameters of both powder and sintered samples were deduced by X-ray diffraction (XRD) and further confirmed with high resolution transmission electron microscopy. Powder diffraction and electron microscopy study show that ball milling of starting elemental powders (V–4Cr–4Ti) with and without yttria addition has resulted in single phase α–V (V–4Cr–4Ti) alloy. Wherein, XRD and electron microscopy images of sintered samples have revealed phase separation (viz., Cr–V and Ti–V) and domain size reduction, with yttria addition. The reasons behind phase separation and domain size reduction with yttria addition during sintering are extensively discussed. Microhardness and high temperature compression tests were done on sintered samples. Yttria addition (0.3 and 0.6 at.%) increases the elevated temperature compressive strength and strain hardening exponent of α–V alloys. High temperature compression test of 0.9 at% yttria dispersed α–V alloy reveals a glassy behaviour.     

V-5Cr-5Ti合金弹性和力学性质的第一性原理研究

V-5Cr-5Ti合金作为核聚变堆第一包层的主要候选结构材料之一,但对其力学性质的理论研究相对较少.采用随机固溶体模型,利用第一性原理方法计算出V-5Cr-5Ti合金的弹性常数、体模量、剪切模量、杨氏模量、泊松比和柯西压力等,并与计算出的纯钒的相关数值进行对比,结果表明V-5Cr-5Ti合金具有良好的塑性和强度,但其塑性要略低于纯钒的.并对加入氧原子后的V-5Cr-5Ti合金进行了相关计算,通过对比计算结果发现,由于氧原子的加入,使V-5Cr-5Ti合金的塑性和强度都出现了不同程度的降低.最后对V-5Cr-5Ti合金和纯钒的理论强度进行了计算,并绘制出两者的应力-应变关系图,通过对比再次验证了上面的结论.     

Influence of phosphorus on the development of nickel alloy/h-BN-based self-lubricating composites processed by powder metallurgy

The purpose of this work was to evaluate the influence of phosphorus quantity of the matrix of a nickel alloy on microstructure and hardness of nickel composite with hexagonal boron nitride – h-BN. The work was carried out using two nickel alloys with varying quantities of phosphorus (0.3 and 0.75 wt.%). The quantity of particles of solid lubricant added to the alloy was 10 vol.% of h-BN. The samples were compacted at 600 MPa and sintered at 1150?°C for 60 min in plasma. The results showed that the composite with 0.3 wt.% of phosphorus had hardness of 236 HV 0.025 (±34,25) and the composite with 0.75 wt.% of phosphorus had hardness of 326 HV 0.025 (±38,90), and formation of pellets of h-BN with a size between 50 and 100 μm and low porosity due to the formation of liquid phase of phosphide during sintering which carries the lubricant fine particles of approximately 10 μm dispersed in the microstructure during pore coalescence. As a result, the quantity of phosphorus present may influence the microstructural properties (pore number and size and distribution of particles of solid lubricant) and hardness which are so important for the development of self-lubricating composites, particularly, the nickel alloy/h-BN composites.