High-temperature tensile properties of in situ-synthesized titanium matrix composites with strong dependence on strain r
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Minmin Wang, Feng Zhu, and Bo Ji Department of Titanium Alloy, Special Steel Branch, Baoshan Iron and Steel Co. Ltd., Shanghai 200940, People’s Republic of China (Received 14 April 2008; accepted 12 August 2008)
High-temperature titanium matrix composites reinforced with hybrid reinforcements are synthesized by common casting and hot working technologies. Tensile properties are tested at different temperatures and strain rates. Ultimate strengths of the composites are significantly enhanced under all conditions and decrease when the strain rate is lower. Equicohesive temperature of the matrix is around 873 K at the strain rate 10−3s−1 and well below 873 K at 10−5s−1. At higher temperature or lower strain rate, interfacial debonding is more drastic and reduces the strengths of composites. The materials are embrittled under creep-rupture conditions. Strict reinforcement morphology is required for more complex service conditions at high temperatures in metal matrix composites.
I. INTRODUCTION
Application of high-temperature titanium alloys is limited by their performance at high temperatures. The upper limit of the service temperature is 873 K for the commercially applied high-temperature titanium alloy IMI834. In recent studies, titanium matrix composites (TMCs) provide great improvement in properties and service temperature for the high-temperature titanium alloys.1–4 Conventional technologies like common casting, mechanical alloying, and powder metallurgy can be introduced to the in situ synthesis of discontinuous whisker or particle-reinforced TMCs,5–9 which greatly save the costs of production. Thus, in situ-synthesized TMCs exhibit considerable potential in aerospace and military application. Among the discontinuous reinforcements in in situsynthesized TMCs, TiC and TiB are proved to be the best due to the high-strength, high-thermal stability and similar thermal expansion coefficient to titanium.8–14 Rare earth elements, which effectively improve the thermal stability of titanium alloys,15,16 are also considered favorable. In situ synthesis of TMCs with hybrid and multidi-
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Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2008.0378 3066
http://journals.cambridge.org
J. Mater. Res., Vol. 23, No. 11, Nov 2008 Downloaded: 18 Mar 2015
mensional reinforcements was realized, and the tensile properties were tested at both room and high temperatures in literature.17–23 In the previous research,24 the effect of reinforcements on tensile properties of TMCs at high temperatures was studied. The tests were conducted at a constant strain rate 10−3s−1 (usually for testing the quasistatic strength of engineering material). However, it is necessary to study the reinforcing effect at different strain rates to apply such TMCs under complex service conditions. In the present study, high-temperature TMCs reinforced with hybrid reinforcements are in situ synthesized by common casting and hot working technologies. Tensile properties are tested at different temperatures and strain rates
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