Z.H. Wang

Nanoindentation characterised plastic deformation of a Al0.5CoCrFeNi high entropy alloy

Abstract The plastic deformation of a high entropy alloy Al0.5CoCrFeNi was investigated by instrumented nanoindentation over a broad range of strain rates at room temperature. Results show that the creep behaviour depends on the strain rate remarkably. In situ scanning images showed a significant pile up around the indents, demonstrating that a highly localised plastic deformation occurred in the process of nanoindentation. Under different strain rates, contact stiffness and elastic modulus basically remain unchanged. However, the hardness decreases as indentation depth increases due to indentation size effect. For the same maximum load, serrations became less prominent as the loading rate of indentation increased. Similar serrations have been observed in the current alloy upon quasi-static compression.

Superior Mechanical Properties of AlCoCrFeNiTi x High-Entropy Alloys upon Dynamic Loading

High-entropy alloys with composition of AlCoCrFeNiTix (x: molar ratio; x = 0, 0.2, 0.4) under quasi-static and dynamic compression exhibit excellent mechanical properties. A positive strain-rate sensitivity of yield strength and the strong work-hardening behavior during plastic flows dominate upon dynamic loading in the present alloy system. The constitutive relationships are extracted to model flow behaviors by employing the Johnson-Cook constitutive model. Upon dynamic loading, the ultimate strength and fracture strain of AlCoCrFeNiTix alloys are superior to most of bulk metallic glasses and in situ metallic glass matrix composites.

Microstructure and wear behavior of Ti-6Al-4V treated by plasma Zr-alloying and plasma nitriding

A duplex treatment of plasma Zr-alloying and plasma nitriding was used to improve the tribological properties of Ti-6Al-4V. The microstructure of the Zr-N composite (alloyed) layer formed on Ti-6Al-4V and its hardness, friction and wear properties were investigated by using OM, SEM, GDOES, EDS, microhardness tester as well as ball-on-disk tribometer. The results of microstructural analysis show that the alloyed layer is compact and uniform and is mainly composed of ZrN, TiN0.3 and AlN. A very tiny adhesive and slight oxidation wear is the primary wear mechanism for the modified Ti-6Al-4V. The tribological property is improved significantly after the duplex treatment. The good combination of antifriction and wear resistance for modified Ti-6Al-4V is mainly attributed to the higher surface hardness of metal nitrides formed on the surface and enhanced supporting of the Zr-diffusing layer.

Plasma Niobium Surface Alloying of Pure Titanium and its Oxidation at 900 °C

Abstract A niobium-modified layer on pure titanium surface was obtained by means of double glow plasma surface alloying technique. The modified layer was uniform, continuous, compact and well adhered to the substrate. The niobium composition in the modified layer decreased gradually from the surface to the substrate. The oxidation behavior of the niobium-modified layer was investigated and compared with the untreated surface at 900 °C for 100 h. Characterization of the layers was performed using X-ray diffraction and scanning electron microscope, respectively. The test results show that the oxidation behavior of pure titanium was improved by niobium alloying process. Niobium has a positive influence on the oxidation resistance.

Wear and corrosion properties of Mo surface-modified layer in TiNi alloy prepared by plasma surface alloying

In order to improve the wear resistance and restrain nickel release of TiNi alloys, the Mo modified layers on TiNi substrates were obtained using the double glow plasma surface alloying technique. Scanning electron microscopy (SEM), glow discharge optical emission spectroscopy (GDOES) and X-ray diffraction (XRD) were employed to investigate the morphology, composition and structure. Microhardness test and scratch test were performed to analyze the microhardness and coating/substrate adhesion. Tribological and electrochemical behaviors of the Mo modified layers on TiNi were tested by the reciprocating wear instrument and electrochemical measurement system. The Ni concentrations in Hanks’ solution where surface electrochemical tests took place were measured by mass spectrometry. The surface-modified layer contained a Mo deposition layer and a Mo diffusion layer. The X-ray diffraction analysis revealed that the modified layers were composed of Mo, MoTi, MoNi, and Ti2Ni. The microhardnesses of the Mo modified layers treated at 900 °C and 950 °C were 832.8 HV and 762.4 HV, respectively, which was about 3 times the microhardness of the TiNi substrate. Scratch tests indicated that the modified layers possessed good adhesion with the substrate. Compared with as-received TiNi alloy, the modified alloys exhibited significant improvement of wear resistance against Si3N4 with low normal loads during the sliding tests. Mass spectrometry displayed that the Mo alloy layers had successfully inhibited the Ni release into the body.

Dynamic Deformation Behaviors of an In Situ Ti-Based Metallic Glass Matrix Composite

Quasi-static and dynamic deformation behaviors, fracture characteristics, and microstructural evolution of an in situ dendrite-reinforced metallic glass matrix composite: Ti50Zr20V10Cu5Be15 within a wide range of strain rates are investigated. Compared with the quasi-static compression, the yielding stress increases, but the macroscopic plasticity significantly decreases upon dynamic compression. The effects of the strain rate on strain hardening upon quasi-static loading and flow stress upon dynamic loading are evaluated, respectively. The Zerilli-Armstrong (Z-A) model based on dendrite-dominated mechanism is employed to further uncover the dependence of the yielding stress on the strain rate.

Evolution of hardness and modulus within a cold-rolled in situ dendrite-reinforced metallic glass matrix composites

Abstract Cold-rolled in situ dendrite/metallic glass matrix (MGM) composites with a composition of Ti48Zr18V12Cu5Be17 exhibit a fact that modulus and hardness of matrix is decreased with the increasing in thickness reduction, while the modulus of dendrites remains constant, and hardness tends to increase sharply with the increase in thickness reduction < 30% and then it approximately remains constant. Free volumes created by plastic deformation lead to the decrease of the matrix modulus. Dendrites are restricted by surrounding matrix, which results in the modulus of dendrites constant. Multiplication of shear bands is the dominant mechanism affecting the hardness of the matrix. The present study gives a guideline to predict the evolution of hardness and modulus in both dendrites and glass matrix in such dual-phase composites.

FRICTION AND WEAR BEHAVIORS OF Ti6Al4V ALLOY TREATED BY PLASMA Ni ALLOYING

The Ni modified layer was prepared on surface of the Ti6Al4V substrate by plasma surface alloying technique (PSAT). The cross-section micro structure, phase structure and microhardness of Ni modified layer were studied. The friction and wear behavior of the Ni modified layer and the Ti6Al4V substrate were analysed. The effects of displacement amplitude, frequency and fretting time on friction coefficient of the Ni modified layer were investigated. The results indicated that the wear rate was lower compared with that of the Ti6Al4V substrate. Friction coefficient of the Ni modified layer increased with the increase of frequency. But it was insensitive to the change of wear time and the displacement amplitude. The wear mechanism of the Ti6Al4V was adhesion and abrasion wear mechanism while the Ni modified layer showed slightly abrasion wear.

HIGH-TEMPERATURE TRIBOLOGICAL BEHAVIORS OF TINI/TI2NI ALLOYED LAYER ON SURFACE OF TI6AL4V ALLOY

Plasma surface alloying (PSA) technique was employed with nickel as incident ions to prepare the TiNi/Ti2Ni alloyed layer on surface of Ti6Al4V. High-temperature friction and wear performance of TiNi/Ti2Ni alloyed layer and the Ti6Al4V substrate were evaluated at 500∘C. The results indicated that the TiNi/Ti2Ni alloyed layer exhibited superior high-temperature wear performance. The variations of friction coefficient were the same rule but wear rate was lower compared to Ti6Al4V substrate. The wear mechanism of TiNi/Ti2Ni alloyed layer was mainly slight abrasion and the Ti6Al4V substrate showed abrasion and oxidation wear. The friction coefficient of the TiNi/Ti2Ni alloyed layer decreased from 0.90 to 0.50 with the increase of temperature from room temperature to 500∘C.

SURFACE Nb-ALLOYING ON 0.4C–13Cr STAINLESS STEEL: MICROSTRUCTURE AND TRIBOLOGICAL BEHAVIOR

0.4C–13Cr stainless steel was alloyed with niobium using double glow plasma surface alloying and tribological properties of Nb-alloyed steel such as hardness, friction and wear were measured. Effects of the alloying temperature on microstructure and the tribological behavior of the alloyed steel were investigated compared with untreated steel. Formation mechanisms of Nb-alloyed layers and increased wear resistance were also studied. The result shows that after surface Nb-alloying treatment, the 0.4C–13Cr steel exhibits a diffusion adhesion at the alloyed layer/substrate interface and improved tribological property. The friction coefficient of Nb-alloyed steel is decreased by about 0.3–0.45 and the wear rate after Nb-alloying is only 2–5% of untreated steel.