The Microstructure And Performance Of Ni/TiC Functional Gradient Materials By Direct Laser Fabrication

Functionally gradient materials (FGM) is on the basis of the computer aideddesign (CAD) materials using the advanced materials'composition technology,which makes the compositions elements (component and structure, etc.) changecontinuously from one side to the other side along the thickness direction. And itwill be a designed new type material with a gradient changes on the properties andfunctions of the materials with the wide application prospects. The directly laserfabrication (DLF) technology, based on the three-dimensional metal parts directlyfabrication technology of the laser cladding, is a kind of advanced manufacturingtechnology developed in the middle and later period of 1990s. It combines therapid prototype technology and the laser cladding technology and can fabricate allkinds of complicated net shape fully dense metal parts from CAD directly withoutthe aiding of cutting tool and die. Due to the advantages of good parts performance,high fabrication flexibility, short production cycle and lower cost, has been widelyrecognized by the academic field and manufacturing industry'attentions.Ni/TiC has been become the research hotspots of high-temperature structuralmaterials because of its high specific strength, high-temperature resistance,corrosion resistance and etc. This paper is mainly aimed at the preparation of theinterface interlayer between Ni (at one side) and TiC (at the other side) whichcontains both the advantages of Ni and TiC. The thermal physical properties difference between the outer ceramics and the inner metal can obtain fullcompensation due to the interface interlayer, hoping to get the advances materialswith properties of higher strength, better fracture toughness and the thermal stressrelaxation, and providing the significant references for the FGM.For one hand,the DLF technology is presented to fabricate Ni/TiC FGM for thispaper. The XRD result indicate that FGM are composed with TiC and Ni. In thisthesis,the structure of Ni/TiC FGM, which were prepared using the advanced DLFtechnology,is studied.Both Ni/TiC FGM and the corresponding homoge neouscomposite materials are constituted of ceramics phase of fcc TiC and metal phaseof Ni,and the structure of Ni/TiC FGM exhibits the macroscopical inhomogeneityand microstructural continuity.The gradient layer interfaces combineexcellently,and the microstructure exhibits gradient distribution withoutmacroscopical interfaces.The TiC grains ,whose volume increases with theincreasing content of Ni , are mostly quasi -rotundity. The comparative analysisbetween the microstructures in each gradient layer of the FGM and those in thecorresponding homogeneous composite materials showed that one can evaluate theperformance of the gradient materials by the approach to evaluate the performanceof the homogeneous composite Ni/TiC materials.For the othe hand, by different experimental methods the physical andmechanical properties of each layer in the Ni/TiC FGM are evaluated. The resultsshow that there appear the continuous gradient changes with the Ni contentchanging in each layer composition materials, w hich is consitient with thedesigner idea. The fractures of different materials present the changes from thetoughness to the brittleness with the changes of the Ni volume fraction. Moreover,the thermal stress mitigating effect is confirmed by the observation of cracks afterthermal fatigue and thermal shake in experiments. The directly laser fabrication technology can meet the demand of the gradient materials.In a whole, the paper adopts the high flexibility and toughness processingcharacteristics to realize the continuous gradient change'transition region betweenthe TiC ceramics and the Ni metal, which makes the FGM have the good thermalstress relaxation and the resistance to heat shocks and avoid the interface stressdue to the mismatch of the thermal physical properties difference between theouter ceramics and the inner metal. The experiment results verify the feasibility ofthe materials system, the design composition distribution and the used fabricationmethod. It can make full use of the advantages of the ceramics high temperatureresistance and the metal strong bearing. It reaches the aim of the complementaryamong the properties and it accord with the research standards of the FGM.