Processing, Microstructure and Mechanical Properties of in Situ Al‐based Metal Matrix Composite Reinforced with 22 wt%WAl₁₂ Particles

Abstract

In the past decade, Al-based metal matrix composite (MMC) reinforced with particles has been received much attention due to its high elastic modulus, high strength and light weight that is of value to automobile and aerospace industries, etc. [1] Very recently, Yu et al [2] reported the structure and characterization of an in situ Al-based MMC reinforced with Al 2 O 3 and TiC produced by hot isostatic pressing (HIP) technique, which indicated that the mechanical performance of Al-10 wt%TiO 2 -1.5 wt%C is higher than that of Al-10 wt%TiO 2 due to formation of TiC and elimination of large intermetallic Al 3 Ti plates. By using a mechanical alloying technique, Jia et al [3] synthesized an Al 3 Ti particle and Nb flake reinforced Al matrix composite and found that the MA Al-12Ti-Nb has much more excellent mechanical properties and thermal stability than the MA Al-12Ti. Al-TiB 2 metal matrix composites prepared by exothermic reactions at 850°C using K 2 TiF 6 and KBF 4 salts and using stir cast route at above 1000°C, respectively, have also been documented by Lu's group. [4,5] Compared with these typical ceramic particulates, in situ intermetallic WAl 12 , fabricated by MA and vacuum hot pressing (HP) techniques, is a new reinforcement with clean grain boundary. However, synthesis of composites with in situ WAl 12 reinforcement has never been reported.Mechanical alloying is a solid-state powder processing technique which was effectively employed to prepare a variety of alloy powders or blend green samples, [6][7][8][9] The hotpressing technique is a highly evolved method of preparing full dense, good matrix-to-reinforcement compatible and microstructural homogeneous materials. Therefore, MMCs can be well synthesized by using the in situ technique. [3] In this paper, we focus on fabricating in situ WAl 12 reinforced Al-based MMC via MA and HP using W 14 Al 86 alloy, which is of high microhardness, good oxidation resistance and low density, etc. [10] The mechanical properties and the microstructures of the MMC were also determined.Results and discussion. Synthesis of W 14 Al 86 alloy: The aluminum and tungsten powders were mixed to give a desired composition of W 14 Al 86 and mechanically milled for 10, 30, 50 and 70 h respectively in a stainless steel vial filled with argon. Figure 1 shows a series of XRD patterns indicating the phase evolution as a function of milling time in the mixture. The as-received elemental blend showed the presence of both elemental aluminum and tungsten phases clearly. As milling time increased, intensity of Al peaks decreased continuously. After 70 h milling, Al peaks disappeared, whereas W peaks were still visible. It implied that Al completely dissolved in the remaining bcc W-based phase, indicating that W 14 Al 86 alloy was prepared by mechanical alloying process.Formation of in situ WAl 12 reinforcement: Figure 2 shows the typical XRD patterns of the HPed Al-15 wt%W 14 Al 86 samples under various sintering conditions. After sintering at 600 for 30 min ( Fig. 2(a)), the diffraction peaks ...