Effect Of Adding Elements On The Surface Microstructure And Oxidation Resistance Of TiAl-based Alloys

Miedima model and Kolher models, had been used to study the the chemicalreaction and diffusion ability of each element in TiAl alloys interface reactions ofinvestment casting. a certain proportion of Si and Mo powder is added to therefractory material of the mould shells surfacethe to cast Ti-47Al andTi-48Al-2Cr-2Nb alloys, comparative study of various kinds of alloy of theinterface reaction, and through the three-point bending experiment studies themechanics properties of the interface reaction layer. The Ti-47Al andTi-48Al-2Cr-2Nb alloys casted in new mould shells were studied aboutoxideoxidation surface morphology, element distribution and hickness of theoxideoxidation layer after oxided different time at800℃, and contrast oxidationresistance of the shell casting of didn’t add elements on the surface ofTi-47Al-0.5Si and Ti-47Al-2Mo alloys..Calculation and analysis showed that if Si element was added in the TiAlalloys, binding force between the Ti and Al elements would decrease. Si was apt toparticipate in chemical reactions and diffuse in the TiAl alloys. When Mo elementwas added in the TiAl alloy, The binding force of Ti and Al element wouldincrease, The chemical reaction and diffusion ability of Mo element in TiAl alloyis poor. When Cr and Nb elements were added in the TiAl alloys, the bindingforce between the Ti and Al elements were incresed, the binding force between Tiand Si elements function was relatively complex. On the whole, the chemicalreaction and diffusion ability of Si element was suppressed; When Cr and Nbelements were added in the TiAl alloys, the binding force between Ti, Al and Ti,Mo elements would increase at the same time. The effect is relatively complex andneeded to be determined by experiments.Studies had shown that the mould shell whose surface added Si elementcasted Ti-47Al alloy, the interface reaction was acute and a lot of TiSi2phaseappeared in the reaction layer, the depth of the element diffused of100microns;When casted Ti-48Al-2Cr-2Nb alloy, its interface reaction degree were relativelylight, the spread of the elements in basic alloy was slightly. The mould shellsurface added with Mo element added casted Ti-47Al and Ti-48Al-2Cr-2Nb alloys,the interface reaction and the element diffusion degree was less, but the thermalexpansion coefficient between the layer containing Mo element and substrate isdifferent. A large number of micro-cracks appeared in the alloy surface. The castedsamples were tested by three-point bending experiments. Si element makes the alloy layer brittleness increases and Mo element makes reaction layer plasticincreases, but as a result of adding Mo element. there were a large number ofmicro-cracks existed in the alloys surface, so the mechanical properties of alloyscasted in the mould shell added elements are significantly reduced.Experiments show that TiAl alloys casted in the mould shell added Si elementtreated by high temperature oxidation with different time, the size of the TiO₂onthe surface of oxidation layer were refined and the thickness of oxidation layer isdecreased and the sustained oxidation resistance ability increased obviously; TiAlalloys casted in the mould shell added Mo element treated after high temperatureoxidation appeared different degree of oxidation of spalling phenomenon, itsdegree of spalling had a lot to do with the alloy composition and mass fraction ofMo slement in mould shell surface; The function of oxidatation resistence of TiAlalloys added a small amount of Si and Mo elements were impoved slightly.