| Direct laser fabrication(DLF),booming in the late nineties in the 21st century, combines rapid forming technology with laser cladding and rapid prototype various complex metal parts which are near-shaped and compact from the CAD files without the help of dies and cutting tools. This technology is widely noticed in academe and manufacture industry for many advantages such as high- performance parts, high- flexibility, short forming cycle, low cost, etc. Functional gradient materials (FGM), basing on computer-assistant materials design, can make the properties and functions of materials changing gradient by altering the material elements in thickness continuously with the help of advanced synthesizing technology. Ni/TiC composites have been the focal engineering material under high temperature because of high ratio strength and corrosion-resistance.In this thesis, Ni/TiC FGM which possesses the properties of both Ni and TiC on each side is expected by DLF in order to mitigating thermal stress and resisting heat concussion. The Ni/TiC interface transition layer is gradient so that the properties can change accordingly.Both the thermal stress design and structure optimization play an important role as the base of the research on FGM. In the whole design process, the composition and structure of FGM are optimized by simulate of thermal stress according the practical preparation and working conditions to obtain the eligible material.The key parameters, including composition distribution exponent, the thickness and number of layers, are determined to get the maximum mitigating gradient of FGM stress for Ni/TiC by analyzing the remnant stress results of cooled FGM prepared by DLF. The results shows: when the gradient composition exponent p=1, the minimal remnant stress of FGM can be obtained and the distribution is reasonable. The thinner the layer is, the smaller the remnant stress is. Considering all the factors, 1 is suitable for h. Although the remnant stress gets smaller with the fewer layers, the dropping extent of thermal stress is smaller at the same time, so 11 is the best for n. FGM material is prepared according to the optimized composition distribution and the microstructure is observed. The result shows that the composition distributes gradiently from Ni to TiC. Moreover, the thermal stress mitigating effect is confirmed by the observation of cracks after thermal fatigue and thermal shake in experiments.Birth and death, basing on ANSYS, simulates the detailed producing process of gradient materials, reckons the displace of the laser using cyclic loading, calculates the DLF process, and acquires the variation of the stress field and temperature field resulting from the formation of the gradient materials and the adaptation of laser heat source during DLF process. The results show that temperature suddenly goes up when the laser beam scan to the top of a subject, and then drops to balance, meanwhile temperatures of all layers goes up continuously. On the other hand, the changing of stress field is opposite to that of temperature field described above. The stress is relatively bigger when the laser beam scans to the middle, and it drops abruptly as the laser beam scans to top. After that it increases again until balance. During the process, the stresses of every layer decrease incessantly. Residual stress in this process is smaller than that of DLF process during the entire cooling process.The simulation method mentioned above, basing on ANSYS program, is used to simulate FGS thermal stress of different material under different initial state by changing parts of parameters, and it also offers a general method for structural optimized design of thermal stress released FGM. Furthermore, it can also simulate the temperature field and stress field of different materials which are manufactured by different process parameter by changing some simulating parameters. Moreover, it proposes basic theory and improving direction for the study of parameters of laser process.
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