光电工程, 2017, 44 (12): 1248, 网络出版: 2018-01-17  

Effect of constant temperature substrate on microstructure and hardness of Al2O3-based eutectic ceramics

Effect of constant temperature substrate on microstructure and hardness of Al2O3-based eutectic ceramics
作者单位
Key Laboratory for Precision and Non-Traditional Machining Technology of Ministry of Education,Dalian University of Technology, Dalian 116024, China
摘要
Abstract
Al2O3-YAG eutectic ceramic has been considered as one of the most potential alternatives to current traditional super-alloys applied in the aerospace field due to its extremely excellent high temperature mechanical properties, such as high temperature strength, oxidation resistance and high temperature structure stability. Al2O3-YAG eutectic ceramic thin-wall samples were prepared by laser engineered net shaping using Al2O3and Y2O3 powders as raw materials. During the process of the laser engineered net shaping, the heat transfers to substrate and the heat accumulation is serious. According to this characteristic, a water-cooled constant temperature substrate was designed to change the temperature gradient and the cooling condition in the forming process. Al2O3-YAG eutectic ceramic thin-wall samples forming ex-periments were carried out on a common substrate and a water-cooled constant temperature substrate with the same laser power, scanning velocity, powder feeding rate and Z increment. The common substrate is TC4 substrate, while the water-cooled constant temperature substrate is composed of aluminum alloy cooling block, TC4 substrate, and plastic hose. The thermal plastic ensures the good contact between the TC4 substrate and aluminum alloy cooling block, and the heat accumulated on the TC4 substrate is rapidly dissipated through the aluminum alloy cooling block in which the constant temperature cooling water of 28 ℃ circulates. The Al2O3-YAG thin-wall samples prepared on different sub-strates were obtained, and their macro-morphology, microstructure and microhardness were compared. The results show that the water-cooled constant temperature substrate has a significant effect on the microstructure and eutectic spacing of Al2O3-YAG eutectic ceramic. The microstructure of thin-wall sample prepared on the common substrate is three-dimensional network structure with an average eutectic spacing of 0.96 μm. And the microstructure of top part of the sample prepared on the water-cooled constant temperature substrate is colony structure, while the microstructure of bottom part is dendrite structure which grows in the reverse direction of the heat flow. The average eutectic spacing of samples prepared on the water-cooled substrate has reduced to 0.21 μm. It is concluded that the morphological change of microstructures is mainly related to the degree of supercooling. The decrease of eutectic spacing is mainly due to the fact that the solidification rate is inversely proportional to the eutectic spacing. The applications of water-cooled con-stant temperature substrate can effectively improve the solidification rate, so the eutectic spacing decreases with the increase of the solidification rate. Comparing the microhardness of thin-wall samples prepared on the different sub-strates, the microhardness of the thin–wall sample prepared on the water-cooled constant temperature substrate is in-creased by about 10% due to the increase of the solidification rate and temperature gradient, the decrease of the eutec-tic spacing, grain refinement and the interaction between eutectic phase and cracks.

Hanchao Liu, Fan Lu, Guangyi Ma, Dongjiang Wu. Effect of constant temperature substrate on microstructure and hardness of Al2O3-based eutectic ceramics[J]. 光电工程, 2017, 44(12): 1248. Hanchao Liu, Fan Lu, Guangyi Ma, Dongjiang Wu. Effect of constant temperature substrate on microstructure and hardness of Al2O3-based eutectic ceramics[J]. Opto-Electronic Engineering, 2017, 44(12): 1248.

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