Some useful approximations for wrought aluminum alloys based on monotonic tensile properties and hardness

The objective of the present paper is to derive some useful approximations for estimating the strain‐controlled fatigue properties and cyclic deformation of wrought aluminum alloys from hardness and monotonic tensile properties. A variety of relationships and correlations among monotonic tensile properties, Brinell hardness, cyclic deformation and strain‐controlled fatigue properties are developed for wrought aluminum alloys. A simple method is proposed for prediction of the strain‐life curve requiring only ultimate tensile strength and modulus of elasticity. Prediction capability of the proposed method is evaluated for 25 kinds of wrought aluminum alloys with ultimate tensile strength between 120 MPa and 650 MPa. The proposed method provides good approximations of the strain‐life curve.     

Slurry erosion behaviors of basalt filled low density polyethylene composites

In this study, slurry erosion behaviors of basalt filled low density polyethylene composites were investigated. Pure low density polyethylene and four different compositions of the composites 10 wt.%, 30 wt.%, 50 wt.% and 70 wt.% basalt were used in the study. Slurry wear, tensile strain, hardness and fracture toughness tests were performed on the samples. Samples turns in the abraded slurry media including 50 wt.% Al₂O₃ with nominal particle size of 500 μm and the erosion tests of pure low density polyethylene and basalt filled composites were performed at the contact angles of 15°, 30°, 45°, 60°, 75° and 90° for 30 min. in 3 periods at 500 rpm turning speed (1 m/s speed). It was observed that erosion rate have no effect up to 30 wt.% basalt content. Wear resistance of the composites including over 30 wt.% basalt were micro structural examination of the worn samples showed that the basalt particles on the worn surface can be sustained by matrix. Basalt particles were worn more slowly than that of the matrix. The more the basalt content in the basalt filled low density polyethylene resulted to the lower the tensile strength, tensile strain and fracture toughness, and the higher the hardness. The slurry erosion rate of the basalt filled low density polyethylene composites was getting sharply increase above 30 wt.% basalt content above 60° contact angle.     

Improvement of weld temperature distribution and mechanical properties of 7050 aluminum alloy butt joints by submerged friction stir welding

Submerged friction stir welding (FSW) in cold and hot water, as well as in air, was carried out for 7050 aluminum alloys. The weld thermal cycles and transverse distributions of the microhardness of the weld joints were measured, and their tensile properties were tested. The fracture surfaces of the tensile specimens were observed, and the microstructures at the fracture region were investigated. The results show that the peak temperature during welding in air was up to 380 °C, while the peak temperatures during welding in cold and hot water were about 220 and 300 °C, respectively. The temperature at the retreated side of the joint was higher than that at the advanced side for all weld joints. The distributions of microhardness exhibited a typical “W” shape. The width of the low hardness zone varied with the weld ambient conditions. The minimum hardness zone was located at the heat affected zone (HAZ) of the weld joints. Better tensile properties were achieved for joint welded in hot water, and the strength ratio of the weld joint to the base metal was up to 92%. The tensile fracture position was located at the low hardness zone of the weld joints. The fracture surfaces exhibited a mixture of dimples and quasi-cleavage planes for the joints welded in cold and hot water, and only dimples for the joint welded in air.     

The effect of heat treatment on the toughness, hardness and microstructure of low carbon white cast irons

The effect of destabilisation and subcritical heat treatment on the impact toughness, hardness, and the amount and mechanical stability of retained austenite in a low carbon white cast iron have been investigated. The experimental results show that the impact energy constantly increases when the destabilisation temperature is raised from 950°C to 1200°C. Although the hardness decreases, the heat-treated hardness is still greater than the as-cast state. After destabilisation treatment at 1130°C, tempering at 200 to 250°C for 3 hours leads to the highest impact toughness, and secondary hardening was observed when tempering over 400°C. The amount of retained austenite increased with the increase in the destabilisation temperature, and the treatment significantly improves the mechanical stability of the retained austenite compared with the as-cast state. Tempering below 400°C does not affect the amount of retained austenite and its mechanical stability. But the amount of retained austenite is dramatically reduced when tempered above 400°C. The relationship between the mechanical properties and the microstructure changes was discussed.     

Microstructure-fracture toughness correlation in weld joints of Cr-Mo steel

The strength-toughness-microstructure relationship in relation to the micromechanics of a fracture process has been investigated in the weld joints of two alloys: 0.5 Mo and 2.25 Cr-1 Mo steels. These alloys are extensively used to fabricate super-heater tubes, boilers, piping, gas lines, etc., by welding. The applications require high temperature and pressure to be maintained during service. The crack initiation toughness and tearing resistance were evaluated using crack tip opening displacement/J-integral parameters at different temperatures. Quantitative analysis of micro-structure and fracture surfaces was used to study the micromechanics of fracture process in the heat-affected zone (HAZ) of the alloys. Molybdenum steel exhibited a higher percentage of ferrite and lower martensite content, while the other steel showed aligned carbide as the major constituent. The higher hardness and strength values in the HAZ and welding zone (WZ) of Cr-Mo steel, compared to molybdenum steel, may be attributed to the higher amount of martensite phase in the alloy. The higher initiation toughness at 200° C in both the alloys was reflected in the larger dimple size, compared to the size observed at room temperature. A tendency for void sheet formation was noticed in both alloys. Acicular ferrite and martensite appeared to be the most influential constituents affecting tearing resistance and initiation toughness.     

Low-temperature cyclic crack-growth resistance of hydrogenated welds

We study the influence of chemical and phase composition on the cyclic crack-growth resistance of non-hydrogenated and hydrogenated welded joints in low-alloy steel at normal and low (–70°C) temperatures. It was discovered that the increase in the nickel content from 0.06% to 3.27% induces an increase in impact toughness and cyclic crack-growth resistance at low temperatures which can be explained by the increase in the content of needle ferrite and by the substitution of uniformly distributed residual austenite for the pearlitic component in the zone characterized by the columnar structure of heat treated beads. Hydrogen saturation of the weld metal leads to a decrease in its cyclic crack-growth resistance at normal temperatures and produces almost no effect on this parameter at low temperatures (–70°C). The presence of the second austenitic phase in the low-alloy weld metal decreases its susceptibility to hydrogen embrittlement in the case where finely divided austenite is uniformly distributed over the weld.Karpenko Physicomechanical Institute, Ukrainian Academy of Sciences, L'viv. Translated from Fiziko-Khimicheskaya Mekhanika Materialov, Vol. 31, No. 2, pp. 62–68, March – April, 1995.     

Austempering of spheroidal graphite cast iron

We study gray spherulitic cast iron, its microstructure, hardness ultimate strength in tension, elongation, and impact toughness as functions of the duration of isothermal austenitizing in the bainite region at 350 and 400°C after austenitizing at 900°C. As the temperature of quenching increases from 350 to 400°C, the microstructure of the analyzed cast iron changes from lower to higher bainite and the amount of retained austenite increases (its maximum is attained after 1 h). At the same time, the ultimate strength in tension and hardness decrease, whereas the elongation and fracture toughness increase.Published in Fizyko-Khimichna Mekhanika Materialiv, Vol. 40, No. 4, pp. 79–83, July–August, 2004.     

Mechanical properties of titanium-based Ti–6Al–4V alloys manufactured by powder bed additive manufacture

Additive manufacturing is currently a topic of considerable interest at both academic and industrial levels. While a significant amount of data exists on the mechanical properties and structure–property relationships of traditional wrought alloys, less information is available on alloys manufactured by additive manufacture. This review examines current state-of-the-art manufacture of titanium-based Ti–6Al–4V alloys by powder bed additive manufacture. Published mechanical properties to date are collected which include tensile strength, yield strength, hardness, wear, fracture toughness and fatigue. Differences in microstructure and properties compared to conventional wrought alloys of the same composition are described.     

Preparation and characterization of Ni-Cu-P/CNTs quaternary electroless composite coating

Ni-Cu-P/carbon nanotubes (CNTs) quaternary composite coatings were successfully obtained on low carbon steel matrix by electroless plating. The effects of CNTs concentration in the bath on the microstructure of the composite coatings, CNTs content in the composite coatings and the hardness of composite coatings before and after heat treatment at 400 °C have been studied. In addition, the corrosion resistance of Ni-Cu-P/CNTs composite coatings was evaluated by anodic polarization curves in 3.5 wt.% NaCl solution at room temperature. It was noted that the CNTs concentration remarkably influenced the surface morphology of the coatings. With increasing CNTs concentration, both the CNTs content in the composite coatings and the hardness of composite coatings increased at first and then decreased. And the composite coatings after heat treatment provided higher hardness than the as-deposited coatings. The corrosion resistance of Ni-Cu-P/CNTs composite coatings is excellent compared with that of Ni-Cu-P coatings.     

Mechanical and tribological properties of zinc-aluminium metal-matrix composites

Recently, commercial Zn-Al foundry alloys such as ZA-27 have found increasing use for many applications and have competed effectively against copper, aluminium and iron-based foundry alloys. However, the elevated temperature (> 100°C) properties of zinc-aluminium alloys are unsatisfactory and restrict their use in some applications. One viable approach to improving the elevated temperature properties is to reinforce the zinc-aluminium alloys with alumina fibres. In this investigation, the mechanical properties of a Zn-Al alloy reinforced with alumina fibres were evaluated. Tensile, compression and impact properties were determined at 25, 100 and 150°C. Lubricated wear tests were also performed on the unreinforced alloy and composites. It was found that although fibre reinforcement did result in some improvement of tensile and compression properties at elevated temperatures, the composites had poor toughness and ductility. The presence of a brittle SiO₂ layer at the fibre/matrix interfaces resulted in fibre/matrix decohesion under tensile loading, impairing the performance of the reinforced materials. Some improvement in wear resistance was noted for the composite materials but fibre reinforcement did not yield significant improvement in fatigue resistance.     

Influence of crystallite size on the hardness and fatigue life of steel samples coated with electrodeposited nanocrystalline Ni-W alloys

The present work deals with the effect of crystallite size on the hardness and fatigue life of steel samples coated with electrodeposited nanocrystalline Ni-W alloys. The Ni-W alloys were electrodeposited on steel samples at four different current densities (0.05, 0.10. 0.15 and 0.20 A/cm²) and at a temperature of 75 °C. The crystallite size of the deposit reduced (from 40 to 13 nm) with an increase in current density (from 0.05 to 0.20 A/cm²) due to an increase in the tungsten content (from 0.72 to 9.33 at.%). Ni-W alloy containing 9.33 at.% W and having a crystallite size of 13 nm exhibited the maximum hardness of 638 HV. The alloys, with the crystallite size in the range 40-13 nm, followed the direct Hall-Petch relation, i.e. hardness increased with a reduction in the crystallite size. The coated samples exhibited inferior fatigue lives compared to uncoated samples. This may be attributed to the presence of tensile residual stresses and inherent microcracks in the coatings. Among the specimens coated with Ni-W alloys, as the crystallite size decreased, the fatigue life of the specimen increased owing to the increase in hardness values.     

超高强韧Mg-Gd-Y-Zn-Zr变形镁合金研究进展

超高强韧镁合金的研发对推广镁合金在高技术领域的应用具有重要意义。镁与稀土均是我国的优势资源,因此在我国发展超高强韧稀土镁合金具有得天独厚的优势,其中Mg-Gd-Y-Zn-Zr系变形镁合金因其接近高强铝合金的超高强度和塑性,近年来受到研究者的广泛关注。综述了超高强韧Mg-Gd-Y-Zn-Zr系变形镁合金的合金成分、常规塑性变形工艺、新型剧烈塑性变形工艺和热处理工艺对该合金显微组织和力学性能的影响规律,以及该超高强韧变形镁合金的显微组织特征和强韧化机理。T5峰时效态超高强韧Mg-8.2Gd-3.8Y-1Zn-0.4Zr(质量分数)挤压合金具有双峰分布的晶粒尺寸“软-硬”复合层片微结构,以及由高密度的基面γ′纳米片状析出相和棱柱面β′纳米析出相形成的近连续网状结构,该挤压合金室温拉伸屈服强度、拉伸强度和断裂延伸率分别为466 MPa、514 MPa和14.5%。介绍了哈尔滨工业大学等单位在超高强韧Mg-Gd-Y-Zn-Zr系变形镁合金的规模化制备和应用方面的研究进展,并展望了Mg-Gd-Y-Zn-Zr系变形镁合金的发展趋势。     

Structure and wear resistance of the composite layers produced by glow discharge nitriding and PLD method on AISI 316L austenitic stainless steel

The rapid technical development enhances the demands on constructional materials in terms of their resistance to frictional wear, resistance to corrosion and erosion, high hardness, high tensile and fatigue strength. These demands can be satisfied by e.g. applying various surface engineering techniques that permit to modify the microstructure, phase and chemical composition of the surface layers of the treated parts. A prospective line of the development of surface engineering is the production of composite layers by combining various surface engineering methods. The paper presents the results of examinations of the phase composition and frictional wear resistance of the layers produced by hybrid processes, i.e. such that combined glow discharge assisted nitriding performed at 450 °C and 550 °C with a pulsed laser deposition of boron nitride coatings (PLD method). It has been shown that the boron nitride coatings formed on nitrided AISI 316L steel increase its frictional wear resistance.     

Structure and wear resistance of the composite layers produced by glow discharge nitriding and PLD method on AISI 316L austenitic stainless steel

The rapid technical development enhances the demands on constructional materials in terms of their resistance to frictional wear, resistance to corrosion and erosion, high hardness, high tensile and fatigue strength. These demands can be satisfied by e.g. applying various surface engineering techniques that permit to modify the microstructure, phase and chemical composition of the surface layers of the treated parts. A prospective line of the development of surface engineering is the production of composite layers by combining various surface engineering methods. The paper presents the results of examinations of the phase composition and frictional wear resistance of the layers produced by hybrid processes, i.e. such that combined glow discharge assisted nitriding performed at 450 °C and 550 °C with a pulsed laser deposition of boron nitride coatings (PLD method). It has been shown that the boron nitride coatings formed on nitrided AISI 316L steel increase its frictional wear resistance.     

Effect of saturation parameters on the interaction of titanium alloys with carbon-nitrogen-containing media

We study some specific features of phase formation and gas saturation in the course of chemical and thermal treatment of VT1-0, OT4, and VT14 titanium alloys in carbon-nitrogen-containing (graphite and nitrogen under atmospheric pressure) and nitrogen-containing (molecular nitrogen under atmospheric pressure) media. Saturation was carried out at 750–1100°C, and the time of isothermal holding was 5 or 20 h. We have shown that, irrespective of the composition of the saturating medium, within the range 750–1000°C, the phase composition of coatings is identical and consists of TiN and Ti₂N nitrides. The quantitative proportions between them depend on the temperature and time of treatment. Owing to the specific features of the composition of a carbon-nitrogen-containing medium, the depth of the diffusion sublayer increases, and the stoichiometry of cubic nitride decreases, which leads to an increase in the surface microhardness of nitride coatings. Carbonitride coatings are formed only at high saturation temperature (1100°C). Their maximum hardness is 2.5 GPa higher than that of nitrides formed under similar conditions.Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 40, No. 3, pp. 81–87, May–June, 2004.     

Investigations on B-doped SiO2 thermal protective coatings by hybrid sol-gel method

This study first prepared B-doped SiO₂ coating by hybrid sol-gel method. SiO₂ coatings had been successfully used for thermal protection, but its toughness, oxidation resistance and cost are weak points. Hybrid sol-gel method could prepare ultra thin and low cost SiO₂ coatings on nickel alloys. And doping B could improve the coatings’ toughness and oxidation resistance. Thermogravimetry, differential thermal analysis and Fourier transform infrared spectroscopy were used to investigate the additives’ effect on coatings’ formations at different temperatures. X-ray photoelectron spectroscopy and X-ray diffraction were used to investigate the coatings’ element distribution and phase. The results showed that B-doped SiO₂ thermal protective coatings could withstand 1050 °C, and Si-O-B bond was generated to improve the coatings’ toughness. A crystal mullite phase formed on the coatings’ surface at high temperature by thermal diffusion of Al, which significantly improved B-doped SiO₂ thermal protective coatings’ oxidation resistance.     

Evaluation of mechanical and corrosion biocompatibility of TiTa alloys

As-received and heat-treated Ti40Ta and Ti50Ta alloys were evaluated to determine their corrosion as well as mechanical performances and compared to Ti6A14V, a common material utilized for orthopedic (surgical) implants. Anodic potentiodynamic tests performed in Plasmalyte^TM showed that all samples, except for the Ti50Ta specimen aged at 400 °C for 3 h gave a curve similar to that of Ti6A14V. Optical and TEM microscopy was performed to determine as-received and heat-treated microstructures. As-received materials showed an precipitate in an + and martensite matrix. Samples that were aged at 400 °C increased in the density and the length of the precipitate. Vickers hardness measurements were performed to get an approximation of the tensile strengths. Aged Ti40Ta and Ti50Ta specimens produced the highest tensile values when compared to the Ti6A14V material, representing a 31% and 56% increase for the 3 h samples and an 18% and 58% increase for the 10 h samples. Of all the materials studied the Ti50Ta specimen aged for 10 h exhibited the best biocompatibility showing excellent corrosion resistance combined with the highest tensile strength (1089 MPa and 58% harder/stronger than Ti6A14V). © 2001 Kluwer Academic Publishers     

Mechanical and wear behavior of quenched and tempered alloyed hypereutectic gray cast iron

The effect of tempering temperature (100–600 °C) on the hardness and wear resistance of a series of quenched and tempered hypereutectic alloyed gray cast irons has been studied in this work. Hardness was observed decreases with increase in tempering temperature and this trend is influenced by alloying additions and the volume of graphite flakes. Hardness of alloyed gray irons is also influenced by solid solution strengthening of tempered ferrite and carbide content and their distribution. The wear loss of alloyed cast irons was found to be lowest at a tempering temperature of 100 °C and 400 °C. The optimum tempering temperature is 400 °C with moderate hardness and low wear rate. This has been attributed to strengthening of the matrix at this temperature. Beyond 400 °C, the wear rate increases significantly due to carbide coagulation.     

The effects of heat treatment variables on the microstructure and properties of ultra-high strength steels differing in titanium content

The influences of different austenitizing and tempering temperatures on the microstructure and properties of three experimental ultra-high strength steels (UHS) have been investigated. The steels had different Ti content and were subjected to austenitizing treatment at 900, 1000, 1100 and 1200°C followed by oil quench and tempering at 200, 300, 450 and 600 °C. It has been found that the high temperature (1100 and 1200 °C) austenitizing treatments, alter both microstructure and properties, and depending on the subsequent tempering temperature, may have a beneficial or detrimental influence upon the mechanical properties. Addition of up to 0.011 wt% Ti to the steel composition improves hardness, toughness and tensile strength. This improvement in mechanical properties is obtainable with any subsequent heat treatment. For higher Ti content (0.089 wt%), although some further improvement in hardness and tensile strength was obtained, significant degradation in toughness was achieved, particularly when the steel was subjected to high temperature austenitizing and tempering treatment.     

Mechanical properties of a cold-rolled annealed HSLA steel

Hot rolled strips of an HSLA steel containing niobium and vanadium were cold rolled in the range 15 to 80% and annealed for 1 h at various temperatures from 400 to 700 ° C. The response to the amount of deformation and annealing temperature were studied in terms of changes in its hardness, tensile strength and ductility. Hardness and strength were observed to increase while ductility decreased with the amount of deformation. Although annealing of the steel up to 500 ° C did not show significant changes in its mechanical properties, a sharp decrease in hardness and strength and improvement in ductility were observed on annealing the steel at temperatures greater than or equal to 600 ° C. Microstructural studies showed complete recrystallization in the samples subjected to 60% deformation followed by annealing at 600 ° C.