Fatigue strength dependence on the ultimate tensile strength and hardness in magnesium alloys

The relationships between fatigue strength and ultimate tensile strength as well as hardness have been studied in high-strength NZK alloys (Mg–yNd–zZn–xZr) and other magnesium alloys. In the absence of casting defects, clear linear relationships have been found between the fatigue strength and the ultimate tensile strength and the hardness values in these magnesium alloys in both T4 (solutionized) and T6 (solutionized and aged) conditions. The fatigue strength models developed in this work alloys can be directly applied to other defect-free magnesium alloys.     

Strength of tool materials under single impact loading

The article describes a new method and an installation for determining the strength and crack resistance of brittle tool materials under single impact loading. It also presents data on the metrological characteristics of the installation. The installation is suitable for determining the tensile strength and crack resistance of a number of ceramics, hard alloys of the tungsten-cobalt group, and of polycrystals of superhard materials. The effect of the loading rate on the strength of some materials is demonstrated.Translated from Problemy Prochnosti, No. 7, pp. 33–40, July, 1992.     

SiC晶须增强铝合金复合材料的强化效果研究

考察了几种不同基体和状态的SiC晶须增强铝合金复合材料在拉伸变形过程中流变应力的变化情况,发现复合材料的强化效果与基体强度有关,混合法则(ROM)对复合材料抗拉强度的预测与实验值偏差较大,基体强度高的复合材料在拉伸变形过程中出现低应力屈服现象,复合材料的加工硬化能力明显高于基体,文中对出现这些现象的原因进行了探讨.     

优化耐磨含铝铜基合金的组织与性能研究

对优化设计得到的新型耐磨铜合金的力学性能进行了试验研究。试验结果表明，该种铜合金的耐磨性有明显提高，硬度和抗拉强度均优于某些铜合金，而伸长率却不降低。运用扫描电镜和俄歇电子能谱等分析方法对其显微组织和相结构进行了研究。结果发现，优化铜基合金组织中含有较多的硬质点、减摩相和细化的组织，这些都对提高铜合金的耐磨性十分有利。     

Influence of hot extrusion on microstructure and mechanical properties of tungsten based heavy alloy

Microstructural characterisation and room temperature tensile testing were performed on a series of tungsten heavy alloys extruded at various temperatures. Ultimate tensile strength of the alloys increased with increasing extrusion ratio and with decreasing extrusion temperature down to 600°C. Fracture surface observations indicated that the tensile strength correlated with the tungsten cleavage failure mode. The matrix could inhibit the propagation of cracks initiated in the tungsten particles.

MST/3384     

The effects of the processing variables on the microstructure and tensile properties of naturally aged AA6022 wrought alloys

Abstract

The 6xxx series (Al‐Mg‐Si) alloys have properties of medium to high strength, excellent formability, good corrosion resistance, and weldability. In the present paper, we discuss the tensile properties of T4 heat‐treated AA6022 alloys produced by different fabrication processes, including differences in the homogenization temperature, the hot rolling temperature, the cold rolling reduction ratio, and the solid solution temperature. The analysis was done by differential scanning calorimetry, tensile strength testing, by measuring the electrical resistivity, and optical microscopy. The results indicate that the yield strength and the ultimate tensile strength of naturally aged AA6022 alloys increases with increases in the homogenization treatment temperature, hot rolling temperature, cold rolling ratio and solution treatment temperature.     

挤压变形Al—0．8％Mg—0．6％Si—xSc合金的显微组织与力学性能

本文针对挤压变形Al—0．8％Mg—O．6％Si-xSc合金的显微组织和拉伸性能进行了研究,以确定稀土元素Sc和T6处理对该系合金性能的影响规律。结果表明,加入适量的元素Sc可以有效地细化挤压变形Al0．8％Mg-0．6％Si—xSc合金的组织,提高其室温抗拉强度、屈服强度和断裂伸长率;经过T6处理后,Al—08％Si-0．6％Si—xSc舍金的抗拉强度和屈服强度可得到显著提高;挤压变形Al—0．8％Mg～O．6％Si～xSc合金在拉伸加载条件下主要呈现韧性断裂特征。     

Tensile and fatigue evaluation of Ti–15Al–33Nb (at.%) and Ti–21Al–29Nb (at.%) alloys for biomedical applications

In this work the fatigue and tensile behavior of Ti–15Al–33Nb (at.%) and Ti–21Al–29Nb (at.%) was evaluated and compared to that for other titanium-based biomedical implant alloys, in particular Ti–6Al–4V (wt.%). The mechanical properties of interest were fatigue strength, tensile strength, elastic modulus, and elongation-to-failure. Fatigue stress versus life curves were obtained for tests performed at room temperature in air as well as in Ringer's solution at R = 0.1 for maximum stresses between 35% and 90% of the ultimate tensile strength. The results indicated that the fatigue strength and lives and elastic modulus of these alloys is comparable to that for Ti–6Al–4V (wt.%). Considering the data scatter and deformation behavior, the Ringer's solution did not significantly affect the fatigue behavior. Heat treatment reduced the tensile strength and this corresponded to a reduction in the fatigue strength. The tensile strength of the as-processed Ti-Al-Nb alloys was slightly lower than that for Ti–6Al–4V (wt.%), and the Ti–15Al–33Nb (at.%) exhibited lower strengths and higher elongations than Ti–21Al–29Nb. Based on the current results, it is proposed that titanium–aluminum–niobium alloys will be of considerable future interest for biomedical applications.     

退火对电沉积纳米晶Ni-Mn合金性能的影响

采用脉冲电沉积法制备了纳米晶Ni-Mn合金,测定了退火前后纳米晶Ni-Mn合金的显微硬度和抗拉强度.结果表明:退火后电沉积纳米晶Ni-Mn合金的显微硬度和抗拉强度值均有提高.分析了退火处理对电沉积纳米晶Ni-Mn合金性能的影响.     

The tensile behaviour of rapidly solidified magnesium alloys

In this paper, the microstructure and tensile behaviour of three rapidly solidified magnesium alloys is reported. The alloy's composition, i.e. neodymium content, is observed to have an influence on tensile properties and fracture behaviour. The elastic modulus, yield strength and ultimate tensile strength of the alloy increase with an increase in neodymium content. The ductility of the alloys decreased marginally with an increase in neodymium content. The tensile fracture characteristics of the alloys is highlighted in the light of alloy composition and microstructural effects.     

Al-Zn-Mg-Cu系超高强度铝合金的研究现状与发展趋势

分析了近年来超高强度Al-Zn-Mg-Cu系铝合金的成分设计、工艺优化、显微组织分析、力学性能测试及微量元素的作用，对今后的发展动向提出了一些新的看法：采用传统铸造技术得到的铝合金，Zn含量的最大值在8wt％左右，抗拉强度低于700MPa；采用喷射成形技术，Zn含量最大值能够超过12wt％，同时抗拉强度可达800MPa以上，大大提高了铝合金的强度；超高强度铝合金的固溶强化相主要为MgZn2相；经回归时效处理(RRA)后，合金同时具有T6的强度和T7X的抗应力腐蚀性能；微量元素对超高强度铝合金的组织和性能具有显著的影响。     

Effect of shotpeening on sliding wear and tensile behavior of titanium implant alloys

Titanium has good biocompatibility and so its alloys are used as implant materials, but they suffer from having poor wear resistance. This research aims to improve the wear resistance and the tensile strength of titanium alloys potentially for implant applications. Titanium alloys Ti–6Al–4V and Ti–6Al–7Nb were subjected to shotpeening process to study the wear and tensile behavior. An improvement in the wear resistance has been achieved due to surface hardening of these alloys by the process of shotpeening. Surface microhardness of shotpeened Ti–6Al–4V and Ti–6Al–7Nb alloys has increased by 113 and 58 HV_(0.5), respectively. After shotpeening, ultimate tensile strength of Ti–6Al–4V increased from 1000 MPa to 1150 MPa, higher than improvement obtained for heat treated titanium specimens. The results confirm that shotpeening pre-treatment improved tensile and sliding wear behavior of Ti–6Al–4V and Ti–6Al–7Nb alloys. In addition, shotpeening increased surface roughness.     

Effects of thermo-mechanical processing and trace amount of carbon addition on tensile properties of Cu–2.5Fe–0.1P alloys

The effects of thermo-mechanical processing, including intermediate aging treatment and/or solution heat treatment, and a trace amount of carbon (C) addition were studied on tensile behavior of Cu–2.5Fe–0.1P alloys. In this study, Cu–2.5Fe–0.1P alloy sheets without and with a carbon content of 0.05 wt.% were cast and subsequently rolled and thermo-mechanically treated following various processing routes. The introduction of intermediate aging treatment between cold rolling improved the tensile strength of Cu–2.5Fe–0.1P alloys. Solution heat treatment prior to aging was proved to be detrimental on the tensile strength, probably due to recovery and recrystallization causing the complete loss of work hardening during previous cold rolling. The present study also suggested that two-step aging is more effective in improving the strength of Cu–2.5Fe–0.1P alloys than one-step aging. The effect of C addition on improving the tensile strength of Cu–2.5Fe–0.1P alloys was real but marginal, probably due to the limited solubility of C in Cu–2.5Fe matrix. The effects of intermediate heat treatments between cold-rolling processes on tensile properties of Cu–2.5Fe–0.1P specimens with and without C addition are discussed based on optical, scanning electron microscope (SEM) and transmission electron microscope (TEM) micrographs, and SEM fractographs.     

Hot tensile and fatigue behaviour of zinc–aluminum alloys produced by gravity and squeeze casting

The tensile and fatigue properties of zinc–aluminum alloys (ZA-8, ZA-12 and ZA-27) in squeeze and gravity cast forms have been investigated. Tensile tests were conducted at ambient and elevated temperatures up to 150 °C. At low temperatures, the ultimate tensile strength and yielding strength of the squeeze cast alloys have been found to be superior those of the gravity-cast alloys, as the temperature increased they decreased. In the same way, Brinell hardness of the squeeze cast alloys were obtained at higher values than gravity castings. The fatigue tests were performed at a constant speed of 400 rev/min and under a number of stress levels ranging from 100 to 150 MPa. The fatigue behaviour results of the ZA alloys were similar to obtained from the tensile testing. The squeeze cast alloys exhibited good fatigue resistance in proportion to the gravity castings. Metallography examinations showed that the microstructure of the castings differed according to the method of casting used. It was considered that the mechanical properties of the alloys were affected from these micro-structural changes.     

Influence of minor elements additions on microstructure and properties of 93W-4·9Ni-2·1Fe alloys

Effects of elements rhenium and chromium additions on properties and microstructure of 93W-4·9Ni-2·1Fe alloys were investigated. Optical microscope (OM), scanning electron microscope (SEM) and EDAX energy spectrometer were used to characterize the microstructure and compositions of the alloys, respectively. The tensile strength and elongation of alloys were evaluated using the quasi-static tensile testing machine, and the relative densities of the alloys were evaluated using the Archimedes water immersion method. The experimental results indicated that when elements Re and Cr were in the range of 0–1·0 wt.%, relative density, elongation, tensile strength of 93W-4·9Ni-2·1Fe alloys varied from 99·4%, 26·4%, 997·2 MPa without Re additions to 99·5%, 8·6%, 1161·2 MPa with 1·0 wt.% Re addition, respectively. Rhenium generated solid-solution strengthening, grain refinement, reducing ductile tearing and increasing transcrystalline fracture, which resulted in the ductility reduction and the strength increase of the heavy alloys. With the increase of Cr content from 0–1·0 wt.%, the tensile strength, relative density and elongation of 93W-Ni-Fe alloy reduced from 997·2 MPa, 99·3%, 15% to 844·4 MPa, 95·2%, 5·7%, respectively. Element Cr formed interphases with elements W, Ni, Fe and O and gathered along the interface of the alloys, which induced interfacial cohesion and resulted in lower mechanical properties of 93W-Ni-Fe alloys.     

Mechanical characteristics of tungsten-free hard alloys (review)

Titanium carbide- or carbonitride-base tungsten-free hard alloys with a nickel-molybdenum binder, which can effectively replace tungsten alloys in metal and alloy cutting, are examined. The proper choice of the composition and grain sizes of the carbonitride component allows the bending strength of 1500 MPa and hardness of 90–91 HRA to be reached. High-temperature hardness and fracture toughness are of the same order as those of hard tungsten alloys.     

Relationships between secondary dendrite arm spacing and mechanical properties of Zn-40Al-Cu alloys

Three ternary monotectoid-based Zn-40Al-(1, 2, 3%) Cu alloys were produced by permanent mould casting at different pouring and mould temperatures. The average cooling rate for each alloy was determined. Structure of the alloys was examined using optical and electron microscopes and their hardness, tensile strength, percentage elongation and impact energy were measured. As a result of these investigations the relationships between structure and mechanical properties of the alloys were determined.It was observed that the secondary dendrite arm spacing of the alloys decreased with increasing cooling rate and their hardness, tensile strength, percentage elongation and impact energy increased. Correlation of experimental results showed that the hardness, tensile strength, percentage elongation and impact energy of the alloys could be related to their secondary dendrite arm spacing using straight line equations.     

Strength and ductility of novel Mg-8Sn-1Al-1Zn alloys extruded at different speeds

A novel Mg-8Sn-1Al-1Zn alloy developed for high-speed extrusion was successfully extruded at speeds in a range of 2-10 m/min at a temperature of 250 °C. The effect of extrusion speed on the microstructure and tensile properties of the extruded alloys was investigated. Grain size, recrystallization fraction and texture were found to be greatly affected by the extrusion speed, resulting in tensile properties showing lower strength and ductility as the extrusion speed increased. The strength and ductility of the extruded alloys are also discussed in terms of the formation of double twins during the tensile test.     

Effect of C content on the mechanical properties of solution treated as-cast ASTM F-75 alloys

The mechanical properties of solution treated ASTM F-75 alloys with various carbon contents have been studied. Alloys cast under the same conditions were subjected to solution treatment for several periods and then their tensile properties were evaluated. In the as-cast conditions, the alloys exhibited higher strength values with increasing carbon content whereas their ductility was not significantly affected. For the solution treated alloys, the variation of the strength was characterized by a progressive increase for short treatment times until a maximum value was achieved, which was followed by a diminution in this property for longer treatment times. This behavior was more accentuated for the case of the alloys with medium carbon contents, which also exhibited the highest values of strength. Furthermore, the alloy’s ductility was enhanced progressively with increasing solution treatment time. This improvement in ductility was significantly higher for the medium carbon alloys compared with the rest of the studied alloys. Thus, high and low carbon contents in solution treated ASTM F-75 alloys did not produced sufficiently high tensile properties.     

An Investigation on Hall-Petch Relationship in Electrodeposited Nanocrystalline Cu-Ni-P Alloys

Nanocrystalline Cu-Ni-P alloys with average grain sizes of 7, 10 and 24 nm were synthesized by means of electrodeposition.The grain size dependences of tensile strength and hardness of the nanocrystalline Cu alloys were investigated.The breakdown of Hall-Perch relation was exhibited in both tensile strength and hardness.