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Synthesis and Properties of Cr2AlC Using Mechanically Activated Hot-pressing Technology

Author: YuWenBo
Tutor: LiShiBo
School: Beijing Jiaotong University
Course: Materials Science
Keywords: Mechanical activation hot pressing sintering Cr2AlC Cr2Al Si C solid solution Mechanical properties Oxidation resistance
CLC: TQ174.6
Type: Master's thesis
Year: 2010
Downloads: 69
Quote: 1
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Abstract


The MAX material family, ternary carbides Cr2AlC in having preferred material than the Ti3SiC2 and Ti3AlC2 better high-temperature anti-oxidation and corrosion resistance and has a similar thermal expansion coefficient and most of the alloying materials to become a high-temperature structural ceramic member and the coating. Adopted by hot pressing, hot isostatic pressing and pulse discharge sintering technology to prepare Cr2AlC materials, there is a high sintering temperature (1300-1450 ° C), low density (-95%), and the impurity phase (Cr7C3, or Al4C3) and other issues. In order to solve the above problems, the main purpose of the paper is prepared at lower temperatures, dense fine-grained Cr2AlC ceramic block the synthesis of mechanical activation hot comparative study, prepared by hot pressing the coarse grain Cr2AlC material performance. Cr, Al, and C is the molar ratio of 2:1.2:1 mixed powder of high energy ball milling 3h, in the temperature range of 600-1100 ° C, Ar protective atmosphere, 30MPa pressure hot pressing sintering 1h. The results show that the grain size of about the 2μm Cr2AlC single phase block (referred to the fine grain Cr2AlC) in the 1100 ° C was successfully synthesized. Hot pressing technique, using the same ingredients as above 1450 ℃-30MPa-1h conditions synthesis single phase Cr2AlC, grain size of 35 micron (referred to as the coarse grain Cr2AlC). Compared to the hot technology, mechanical activation hot synthesis, synthesis temperature reduction of 350 ° C; the fine grain Cr2AlC material relative density of 99%, higher than the 95% of the coarse grain materials. And flexural strength and Vickers hardness of fine-grained material, respectively, 513 MPa and 6.4 GPa, higher than the coarse grain Cr2AlC 305 MPa and 3.5 GPa. The fine-grained Cr2AlC material oxidation 100h at 900-1200 ° C temperature range, the results show that the Cr2AlC has excellent antioxidant properties, mainly due to the dense layer of alpha-Al 2 O 3 protective layer is formed during the oxidation. Using scanning electron microscopy and energy dispersive analysis of the morphology, composition of the oxide layer has been observed and analyzed. In addition, the study carried out for the first time the use of Si replace part of the Al (Si) C solid solution Cr2Al. The results showed that the Cr/1.1Al/0.2Si/C mixture (molar ratio) in the 1450 ° C .30 MPa the-1h conditions under is thermocompression burning for binding to become Cr2Al (Si) C solid solution. The solid solution material flexural strength, fracture toughness and Vickers hardness was 354MPa, 6.6MP 'am1/2- and 3GPa. Especially solid solution materials exhibit good damage tolerance and micro plasticity at room temperature. Grain spallation, bend, kink, the crack deflection multiple energy-absorbing mechanism given the performance of the solid solution.

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