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Key engineering materials
Trans Tech Publications Ltd.
Key engineering materials

Trans Tech Publications Ltd.

半月刊

1013-9826

Key engineering materials/Journal Key engineering materials
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    High Temperature Mechanical Properties of Ti(C,N)-Co-Mo_2C Cermets

    A. Gallardo-LopezA. Morales-RodriguezA. Dominguez-RodriguezJ. M. Cordoba...
    83-88页
    查看更多>>摘要：The creep behavior of a TiC_xN_(1-x)-Co-Mo2C cermet has been investigated at temperatures between 1100-1200℃ in an inert atmosphere to assess the one step mechanically induced self-sustaining reaction synthesis and pressureless sintering process, and the influence of the Mo_2C additive in the high temperature mechanical properties of this cermet. The samples deform plastically at the chosen temperatures, and values of the stress exponent (n=1.7±0.6) and activation energy (Q=4.3±0.5 eV) have been estimated from uniaxiai compression tests. No significant grain growth has been detected after deformation. The reproducibility of the creep tests compared to other compositions indicates that the Mo_2C addition contributes to increase notably the resistance to high temperature oxidation of the samples, so that the plastic behavior is not affected by oxidation when deformation experiments are performed in an inert atmosphere.
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    • NETL
    • NSTL
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    High-Temperature Mechanical Spectrometer for Internal Friction measurements

    P. SimasJ. San JuanR. SchallerM.L. No...
    89-95页
    查看更多>>摘要：A new high temperature mechanical spectrometer, based on an inverted torsion pendulum, has been constructed for the measurement of the internal friction and the dynamic shear elastic modulus in two different working modes: (a) as a function of temperature (300 - 1800 K) at imposed frequency, during heating or cooling; and (b) as a function of frequency (10~(-3) - 10 Hz) in isothermal conditions. The whole installation is computer controlled by a dedicated software specifically developed. We describe the different parts of this new installation, as well as its performances in both temperature and frequency through an original example study on a high temperature structural intermetallic of Fe-Al.
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    • NETL
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    Influence of the Martensitic Transformation on the Fatigue Life of Austenitic Stainless Steels

    G. FargasM. AngladaA. Mateo
    99-104页
    查看更多>>摘要：The martensitic transformation in austenitic stainless steels can be induced by plastic deformation at room temperature. The benefit of this transformation is commonly used to strengthen stainless steels grades, i.e. their yield and tensile resistance can be adjusted according to the requirement by cold rolling. In this paper, the martensitic transformation was induced by means of torsion deformation. Several torsion angles were selected to achieve different percentages of martensite at the surface of the specimens and then the effect on the fatigue life of the steel was studied. Fatigue testing results showed dissimilar behavior depending on the stress ratio (R) applied during the test. As a conclusion, the presence of martensite in the surface increases the fatigue life for high stress ratios (R=0.8), while at low R values martensitic transformation has no positive effect.
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    • NSTL
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    Tensile behaviour of 6082 aluminium alloy sheet under different conditions of heat treatment, temperature and strain rate

    I. TorcaA. AginagaldeJ. A. EsnaolaL. Galdos...
    105-112页
    查看更多>>摘要：Aluminium alloys are more and more important for the automotive industry due to their high strength to weight ratio and their elevated ductility; they are used for many different parts in automobiles as exterior panels, structural parts, brake housings and others. However, their formability at room temperature is limited. This inconvenient can be improved by increasing the forming temperature of the part. That lack of formability has lead to this research project dealing with the tensile behaviour of aluminium alloys sheets, at different conditions of temperature and strain rate. The analyzed material has been 6082 aluminium alloy, under two different heat treatment conditions (O and T6). Material testing has been carried out in a temperature range between room temperature and 250℃, and a strain rate range between 0.001s~(-1) and 0.1s~(-1). Testing samples have been obtained from laminated sheet of 1.5mm thickness. This article shows that the alloy under T6 condition has a reduced formability, even in warm conditions. In order to get higher deformation values an annealed condition is proposed to form the material. The effect of T6 heat treatment and O annealing treatment in the uniaxial warm formability is discussed and a microstructural analysis is also presented in order to understand the differences on the alloy behaviour.
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    Influence of cold work in the elastic modulus of the Ti-16.2Hf-24.8Nb-1Zr alloy characterized by instrumented nanoindentation

    M. GonzalezJ.PenaJ.M. ManeroF.J. Gil...
    113-118页
    查看更多>>摘要：Abstract. Nowadays, β type Ti-based alloys have been developed for load transfer clinical applications due to their superelasticity, shape memory effect, low elastic modulus and high damping capacity [1]. These properties promote bone regeneration and make them promising candidates for being used in load transfer implantology. The objective of the present work is to achieve a material with shape memory properties and/or low elastic modulus. The influence of cold work on the thermoelastic martensitic transformation and elastic modulus of the Ti-16.2Hf-24.8Nb-1Zr alloy has been investigated to determine optimal conditions. The homogenized vacuum arc melted button was heat treated at 1100℃ during 2 hours and quenched. Samples of each alloy were microstructurally and mechanically characterized after being cold rolled from 5 up to 95%. The elastic response for each condition was evaluated by instrumented nanoindentation by using a Berkovich tip and a spherical tip. A decrease in elastic modulus was observed when increasing the cold work percentage. The lowest value, 44 GPa, similar to that of cortical bone, was found in the 95% cold worked condition.
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    • NETL
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    Influence of the milling time on Mechanical and Magnetic properties of Cu_(90)Co_5Ni_5 alloy obtained by Mechanical Alloying

    Marta LopezM. Elena GomezDavid ReyesK. Ramam...
    119-124页
    查看更多>>摘要：The structure, mechanical and magnetic properties of Cu_(90)Co_5Ni_5 alloys produced by mechanical alloying and subsequent cold consolidation and sintering behavior, have been investigated. A system of small Co and Ni magnetic particles embedded in the non-magnetic copper matrix were prepared through a mechanical milling process by using a planetary ball mill under argon atmosphere for 20 to 60 h. The morphology and particles size, phase formation and chemical composition of the alloyed powder samples for each milling time were characterized by scanning electron microscope and powder X-ray diffraction techniques, respectively. After milling for 60 h, a supersaturated solid solution with coercive field H_c with maximum value of 235Oe was obtained. The continuous decreasing trend of saturation magnetization (M_s) with increasing of milling time can be explained by the reduction of copper oxide by (CoNi) oxide formation, confirmed by powder XRD patterns. The XRD analyses of the as-milled samples revealed that the Bragg peaks of FCC-Co changed partially to HCP-Co on increasing the milling time. Cu_(90)Co_5Ni_5 powders cold consolidated and sintered at 650℃ for 1h segregated mainly into two-phases of mixed (fcc,hc)-Co and fcc-CuNi. After sintering, the mechanical properties for 60h milling reached its optimum, 26HV in hardness corresponding to 250MPa as compressive strength. TEM microanalysis of sintered alloys revealed Co cluster of 2 to 5 nm in size separated each one by 10 to 20 ntn in size. The variation of magnetic properties and its dependence on structural-precipitation change with milling time are discussed.
      原文链接:
    • NETL
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    Sliding wear behavior of a duplex stainless steel

    A. MestraG. FargasM. AngladaA. Mateo...
    125-130页
    查看更多>>摘要：Duplex stainless steels contain similar amounts of austenite y and ferrite a. This two-phase microstructure leads to an excellent combination of mechanical properties and corrosion resistance. However, there are few works dealing with the wear behaviour of these steels. This paper aims to determine the sliding wear mechanisms of a duplex stainless steel type 2205. In order to do it, three different sliding velocities (0.2, 0.7 and 1.2 m/s) and six sliding distances (500, 1000, 2000, 3000, 4000 and 5000 m) were selected. The results show that wear rate depends on both sliding velocity and sliding distance. The wear mechanisms detected were plowing, microcracking and microcutting (typical mechanisms of fatigue wear). These mechanisms evolve according to sliding velocity and sliding distance, highlighting a transition zone in which wear rate is reduced.
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    • NETL
    • NSTL
    • Trans Tech Publications Ltd

    Creep behaviour of closed cell aluminium foams from stress relaxation tests

    B. CarcelA.C. CarcelP. Arrue
    131-136页
    查看更多>>摘要：Creep behaviour of closed cell aluminium foams and transitions from power law to power law breakdown (PLB) creep regimes are investigated from results of stress relaxation tests (SRT) carried out on Alporas foams with densities between 0.20 to 0.32 g/cm~3. Tests were carried out at temperatures between 200℃ and 300℃ and stress relaxation was measured from the collapse stress under compression of the foams. Under similar foam density, temperature and stress conditions, the values of strain rate calculated from SRT tests were of the same order of magnitude than those previously reported in the literature from conventional constant load creep tests. Under stress values close to the collapse stress, the creep mechanism seems to follow a PLB regime, with values of the power law exponent n=10-17, much higher than those corresponding to the power law creep in the solid material (n=4.4-6.5) and with activation energy values close to Q = 150 KJ/mol. Having in mind the limitations of available creep models for closed cell foams and the need for additional experimental results, the use of SRT testing would offer advantages for the assessment of the high temperature behaviour of aluminium foams, due to its lower testing times and reduced experimental effort.
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    A study of the mechanical properties and recrystallization of two types of foil of aluminium 1050 A

    J. Perez-llzarbeJ. Fernandez CarrasquillaC. Luis Perez
    137-145页
    查看更多>>摘要：An experimental study of the variation of the mechanical properties of sheets of aluminium alloy 1050A due to heat treatment has been carried out. For this purpose, sheets and foils rolled from continuous casting strip (CCS) and from hot rolling strip (HRS) have been prepared in the laboratory. Initially, CCS and HRS had a thickness of 7,5 mm and 3,0 mm respectively. The final thickness achieved in both cases was 0,20 mm. In order to obtain hardening curves for CCS and HRS sheets and foils, specimens of different thickness were taken during the rolling process. Oven treatments were carried out for drawing softening curves of foils. Foil proceeding from CCS presents hardening due to the precipitation of Al_3Fe particles at a temperature range of 160℃ to 220 ℃. HRS foil has a lower hardening in the same range of temperatures owing to its low supersaturation of Fe. Correlation between ultimate tensile strength Rm and Vickers hardness is studied. Micrographies of optical microscopy are offered at hard and recrystallized conditions.
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    • NETL
    • NSTL
    • Trans Tech Publications Ltd

    Hall-Petch relationship of a TWIP steel

    F. de las CuevasM. ReisA. FerraiuoloG. Pratolongo...
    147-152页
    查看更多>>摘要：The grain size dependence of the tensile properties of a TWIP steel has been determined for a wide range of grain sizes obtained by grain growth after complete recrystallization of cold rolled material. The near-linear stress-strain behaviour typical of either TWIP steels or other materials that deform by twinning has been observed, the work hardening rate being larger for the smaller grain sizes. The Hall-Petch slope increases as a function of strain, from 350 MPa μm~(1/2) for the yield stress to 630 MPa μm~(1/2) for the maximum uniform strain in the tensile tests, ε ≌ 0.40. Profuse twinning is observed in deformed specimens by means of FIB-ISE.
      原文链接:
    • NETL
    • NSTL
    • Trans Tech Publications Ltd