Effect of WC content on glass formation, thermal stability, and phase evolution of a TiNbCuNiAl alloy synthesized by mec
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C. Yanga) School of Mechanical Engineering, South China University of Technology, Guangzhou 510640, People’s Republic of China; and State Key Laboratory of Metastable Materials Science and Technology, Yanshan University, Qinhuangdao 066004, People’s Republic of China
W.P. Chen and X.Q. Li School of Mechanical Engineering, South China University of Technology, Guangzhou 510640, People’s Republic of China (Received 1 May 2007; accepted 2 November 2007)
Amorphous Ti66Nb13Cu8Ni6.8Al6.2 alloy powders with different tungsten carbide (WC) contents were synthesized by mechanical alloying. Outstanding differences in particle size, thermal stability, glass-forming ability, and phase evolution are found for the synthesized Ti-based glassy powders with different WC contents. This is attributed to the fact that the WC was partially alloyed into the glassy matrix and the matrix element Ti was also partially alloyed into the WC particles. The obtained glassy powders exhibit a wide supercooled liquid region above 64 K. Meanwhile, the main crystalline phase is the ductile -Ti with a high volume fraction in the crystallized alloy powders. These two aspects offer the possibility of easily preparing a plasticity-enhanced bulk composite in the supercooled liquid region by powder metallurgy, which couples the nanosized WC particles with in situ precipitated ductile -Ti phase.
I. INTRODUCTION
As a newcomer to the materials family, bulk metallic glass (BMG), with excellent glass-forming ability and high thermal stability, has been developed in the past two decades based on different alloy systems.1 Unlike crystalline materials, BMG lacks atomic periodicity and is free from defects such as dislocations, grain boundaries, and second phases. Due to its amorphous nature, BMG exhibits a high hardness, strength, and yield strength, and high corrosion and wear resistance relative to its crystalline counterpart.1–3 However, the special microstructure also yields low plasticity and toughness, causing catastrophic failure under stress. This limits its application as a structural material. Considering the large improvement in the plasticity and toughness of crystalline alloy when a second phase is introduced, an improvement in the plasticity and toughness of BMG can be a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2008.0087 J. Mater. Res., Vol. 23, No. 3, Mar 2008
achieved by a homogeneous dispersion of insoluble metallic or ceramic particles as reinforcements during melt solidification.4–16 To further improve the plasticity and toughness of BMG, a method of in situ precipitation of ductile phase was recently developed to synthesize BMG composites based on an appropriate choice of alloy composition and well-controlled solidification conditions.17–25 In this case, an outstanding high plastic strain of 30.5% for Ti66Nb13Cu8Ni6.8Al6.2 bulk composite was achieved due to the precipitation of ductile -Ti phase.24 Alternatively, mechanical alloying (MA) and subsequent consolidation, a technique of powder me
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