Effect of deformation mode on the strength of deformation processed Cu-20%Nb composites

It was previously concluded that all f.c.c.-b.c.c. deformation processed composites have larger Hall-Petch slopes than layered composites (1). The present results on rolled versus wire drawn Cu-20%Nb show that the Hall-Petch slopes in deformation processed f.c.c.-b.c.c. composites depend on the mode of deformation processing and presumably the resulting filament morphology. Layered composites appear to be a good approximation to rolled deformation processed composites because of the filaments being essentially planar in both types of composites. Layered composites appear to be a poor approximation to axisymmetrically deformation processed composites because of the convoluted ribbonlike morphology of the filaments in the latter composites as compared to their planar nature in the former composites.     

Effect of hydrogen on the mechanical properties of a deformation processed Cu-20% Nb composite

The influence of H on the mechanical properties of a deformation processed Cu-20% Nb composite was analysed and compared with the results on similarly processed pure Cu and pure Nb. In this composite the matrix phase (Cu) is relatively resistant to H while the filamentary phase (Nb) is highly susceptible to H embrittlement. The results show that H, in an amount equivalent to that which causes embrittlement of pure Nb, causes no significant deleterious influence on the mechanical properties of Cu-20% Nb. Apparently the ductile Cu matrix creates a favourable stress state for the hydrogenated Nb filaments so that they are constrained from fracturing and continue to deform in a ductile manner.     

Cu-15Cr-0.2Zr形变原位复合材料强度和导电性研究

采用冷变形＋适当的中间热处理的方法制备了Cu-15Cr-0.2Zr形变原位复合材料，并研究了微量盈对Cu-15Cr原位复合材料组织和性能的影响。结果表明：合金经室温变形后，Cr相转变成弯曲薄片状纤维，随着应变量的增加，合金的强度提高，导电率下降。添加0．2％盈使Cu-15Cr-0.2Zr在η=6．438时的极限抗拉强度达到1072MPa，导电率达到68.7％IACS。     

Microstructure and strength of a deformation processed Al-20%Sn in situ composite

An Al-20 vol% Sn metal-metal composite was deformation processed by extrusion, swaging, and wire drawing to a total true strain of 7.4, resulting in a microstructure with Sn filaments in an Al matrix. Both the size and spacing of the Sn filaments decreased as deformation processing progressed. The strength of these composites increased exponentially with the reduction in spacing of the Sn filaments. Immediately after deformation, the Sn second phase showed a convoluted, ribbon-shaped filamentary morphology, but the Sn filaments spheroidized during prolonged storage at room temperature. A thermodynamic assessment is presented for this spheroidization phenomenon.     

Microstructure, mechanical properties and electrical conductivity of industrial Cu-0.5%Cr alloy processed by severe plastic deformation

Microstructure, mechanical properties and electrical conductivity of industrial Cu-0.5% alloy subjected to equal channel angular pressing (ECAP) by route A and cold rolling with and without aging treatment were investigated. The lamellar grains in thickness of 100 nm were obtained after eight ECAP passes. They were not further pancake shaped, but fragmentary and obtained less sharp boundaries with more dislocations in addition to cold rolling. After aging at 450 °C for 1 h, high density of dislocations and some coarse grains were observable after ECAP and the additional cold rolling, respectively. The tensile tests show that tensile strength arrived at 460 MPa and 484 MPa after four and eight passes of ECAP, respectively, the corresponding tensile strength increased to 570 MPa and 579 MPa after the additional cold rolling. However, the electrical conductivity was not more than 35% IACS. It was proved that four passes of ECAP followed by 90% cold rolling and aging at 450 °C for 1 h offered a short process for Cu-0.5%Cr alloy to balance the paradox of high strength and electrical conductivity, under which the tensile strength 554 MPa, elongation to failure 22% and electrical conductivity 84% of IACS could be obtained. The high strength was explained by precipitation strengthening and fine grain strengthening.     

Cu-30%Ag复合纳米粉的制备及其导电性能

用气-液两相稳定法在H2＋He混合气氛中制备了Cu-30%（质量分数）Ag复合纳米粉,并用制备的复合纳米粉作为导电相配制了导电浆料。用XRD、HRTEM、DSC-TG、红外光谱、化学分析、氧含量分析和电阻率测定等手段研究了粉体的相结构、表面组成、形貌、粒度、氧化特性和导电性。结果表明制备的复合纳米颗粒具有壳核结构,核为纳米Cu-30%（质量分数）Ag,壳为二乙二醇丁醚醋酸酯分子层和氧化层双层结构,粉体的粒度分布为10～60nm。在空气中,包覆在复合纳米粒子表面的二乙二醇丁醚醋酸酯分子在200℃左右脱附。在温度低于200℃时,气-液两相稳定法制备的复合纳米粉的抗氧化能力比气相稳定法制备的复合纳米粉的抗氧化能力好。Cu-30%（质量分数）Ag复合纳米粉导电浆料在烧结温度200℃、保温时间50min、真空度为5Pa条件下可获得电阻率为（1.56～3.92）×10-4Ω.cm的导电膜。     

Effect of temperature and strain rate on the strength of a PET/glass fibre composite

Constant strain-rate mechanical testing and surface fractography were used to characterize the failure behaviour of a PET/glass injection-moulding compound and of its unfilled matrix material. Parameters for this investigation were temperature and strain rate. The matrix material exhibited a viscous-brittle transition between room temperature and 60° C. Low temperature failure occurred by craze growth, followed by slow and rapid crack propagation. The composite material likewise behaved as a viscous solid at superambient temperatures. Failure at low temperatures and/or high deformation rates occurred by brittle matrix fracture and fibre pull-out. Under these conditions, mechanical properties improved, relative to those at room temperatures. At intermediate temperatures and/or low strain rates, failure occurred via matrix crazing and crack propagation near the fibre ends. An observed serration of the fracture path at high strain rates is suggested to be due to the need for high shear stresses at the fibre-matrix interface.On leave from the Center for Composite Materials and Department of Chemical Engineering, University of Delaware, Newark, Delaware 19711, USA.     

Effect of rapid deformation and temperature on the strength and plasticity characteristics of chromium-nickel-molybdenum steel

The results of mechanical tests of chromium-nickel-molybdenum steel in uniaxial tension in the strain-rate range of 10^–3–510⁴ sec^–1 and at temperatures ranging from 77 to 523 K are presented. The increase in strength and plasticity characteristics with increasing strain rate is confirmed. The results of the investigations conducted contradict the hypothesis of equivalence of the effect of a temperature reduction and increase in strain rate on the mechanical characteristics of metals.Translated from Problemy Prochnosti, No. 9, pp. 17–19, September, 1991.     

Characterization of strength and microstructure in deformation processed Al-Mg composites

The microstructures, mechanical properties and electrical resistivity have been evaluated for deformation processed Al-20 vol%Mg and Al-13 vol%Mg composites. The Mg second phase adopts a convoluted, ribbon shape filamentary morphology after deformation. Both the size and spacing of these filaments decreases with deformation. The strength of these composites increases exponentially with reduced spacing of Mg filaments. The electrical resistivity of these Al-Mg composites is slightly higher than that of pure Al.     

Effects of strain rates on dynamic deformation behavior of Cu-20Ag alloy

Copper alloy is widely used in high-speed railway,aerospace and other fields due to its excellent electri-cal conductivity and mechanical properties.High speed deformation and dynamic loading under impact load is a complex service condition,which widely exists in the field of national defense,military and industrial application.Therefore,the dynamic deformation behavior of the Cu-20Ag alloy was inves-tigated by Split Hopkinson Pressure Bar (SHPB) with the strain rates of 1000-25000 s-1,high-speed hydraulic servo material testing machine with the strain rates of 1-500 s-1.The effect of strain rate on flow stress and adiabatic shear sensitivity was analyzed.The results show that the increase of strain rate will increase the flow stress and critical strain,that is to say,the increase of strain rate will reduce the adiabatic shear sensitivity of the Cu-20Ag alloy.The Cu-Ag interface has obvious orientation relationship with (111)Cu//(111)Ag;((1)11)Cu//((1)11)Ag;((2)00) Cu//((2)00)Ag and[0(1)1]Cu//[0(1)1]Ag with the increase of strain rate.The increase of strain rate promotes the precipitation of Ag and increases the number of interfaces in the microstructure,which hinders the movement of dislocations and improves the stress and yield strength of the Cu-20Ag alloy.The concentration and distribution density of dislocations and the precipitation of Ag were the main reasons improve the flow stress and yield strength of the Cu-20Ag alloy.     

均匀化处理对Cu-20%Fe复合材料组织与性能的影响

Cu-Fe复合材料具有低廉的成本、良好的变形能力和优异的强化效果,从而得到国内外研究者广泛的关注,但Fe在Cu基体中有很高的固溶度,且在低温下很难析出。研究了1 000℃均匀化热处理对Cu-20%(质量分数)Fe复合材料微观组织、力学和导电性能的影响规律。均匀化热处理使发达Fe枝晶发生断裂和球化,这使得在随后的形变过程中Fe纤维的尺寸减小,纤维间距细化14%~24%。经均匀化热处理的试样的强度和导电率都比未经处理的试样高4%~10%,这主要是由于均匀后热处理使得Fe枝晶球化并促进了Fe的析出。     

Effect of microstructure on the high temperature strength of nitride bonded silicon carbide composite

Four compositions of nitride bonded SiC were fabricated with varying particle size of SiC of ∼ 9.67, ∼ 13.79, ∼ 60 μ and their mixture with Si of ∼ 4.83 μ particle size. The green density and hence the open porosity of the shapes were varied between 1.83 to 2.09 g/cc and 33.3 to 26.8 vol.%, respectively. The effect of these parameters on room temperature and high temperature strength of the composite up to 1300°C in ambient condition were studied. The high temperature flexural strength of the composite of all compositions increased at 1200 and 1300°C because of oxidation of Si₃N₄ phase and blunting crack front. Formation of Si₃N₄ whisker was also observed. The strength of the mixture composition was maximum.     

Low temperature thermal conductivity of some composite materials

Thermal conductivity data are presented for several samples: Gd₂(SO₄)₃ 8H₂O pressed powders with and without copper fibres, pressed powders of NaCl and KCl, cloth base phenolic sheet, epoxy resin-bonded glass fibre laminate, and AGOT graphite in the presence of helium gas. Measurements on all samples were made in the 1–4 K range and on the phenolic sheet and glass fibre laminate at 70 K as well.     

Effect of test conditions on the bending strength of a geopolymer-reinforced composite

This paper presents the results obtained for the effects of the loading rate and of the testing temperature on the mechanical properties, particularly on the stiffness and on the ultimate tensile strength, of a geopolymer reinforced with glass or carbon fibres. HIGH-SILICA geopolymer powder from CLUZ- CYECH and two reinforcement fibres (glass fibres—type AR and carbon fibre - HTS 5631) were used. The displacement rate is varied from 0.02 until to 2 mm/s and the testing temperature is increased from the room temperature until the temperature of 300 °C. For the case of geopolymers reinforced with carbon fibres and glass fibres, the increase of the displacement rate from 0.002 to 2 mm/s led to an improvement on the ultimate flexure strength of about 33 and 31%, respectively. The same dependency was observed for the stiffness, with variations of loading rate of 39 and 53%, for carbon fibres and glass fibres, respectively. Increasing the room temperature until the temperature of 300 °C decreases significantly both the ultimate strength and the flexure stiffness for both reinforcements. However, a major drop on both the stiffness and the strength occurred up to 150 °C.