Effect Of Addition Elements On The Microstructure, Mechanical Properities And Interfacial Reaction Of TiAl-based Alloys

In this paper, the effect of the addition of Nb on microstructure andmechanical properties of investment cast Ti-46Al alloys were studied. And theeffect of the addition of W and B on microstructure and mechanical properties ofinvestment cast Ti-45Al-7Nb alloys were studied.9types of zirconia ceramic moldshell containing different addition materials were prepared by adding differentelemental power to shell surface material. The effect of addition elements on shellsurface morphology was researched. Interfacial reaction between zirconia ceramicmold shell and Ti-46Al alloy, Ti-46Al-7Nb alloy was investigated respectively.The production of interfacial reaction was analyzed.It was shown that a coarse nearly lamellar(NL) microstructure was observedin the as-cast Ti-46Al-xNb alloys by adding niobium to Ti-46Al alloy and the grainsizes were250~300μm. Microhardness results indicated that microhardness ofTi-46Al-xNb alloys increases with increasing of niobium addition. The propertiesof room temperature compression indicated that the yield strength of the alloysincreased while both the ultimate compressive strength and compressibilitydecreased with increasing of niobium addition. And the Ti-46Al-7Nb alloysexhibited superior mechanical properties, with the ultimate compressive strengthof1715MPa and the compressibility of24.21%. Scanning electron microscopy(SEM) observation indicated that the fracture mode of Ti-46Al-xNb alloys wasmainly brittle fracture.It was shown that as-cast Ti-45Al-7Nb-xW alloys exhibited coarse nearlylamellar (NL) microstructure after adding tungsten. With tungsten additionincreasing to0.7at%, the most refined grain size of180μm was obtained.Microhardness results indicated that the value of microhardness (392HV) ofTi-45Al-7Nb-1.0W alloy was the highest. The room temperature compression testshowed that the Ti-45Al-7Nb-0.7W alloy exhibited superior mechanical properties,with the ultimate compressive strength of1821MPa and the compressibility of24.47%. Fractography indicated the fracture mechanism of Ti-45Al-7Nb-xWalloys were mainly brittle fracture.It was shown that after adding boron to Ti-45Al-7Nb alloy, the grain sizedecreased with increase of boron addition. The value of the grain size ofTi-45Al-7Nb-1.0B was only60~70μm. Microhardness results indicated thatmicrohardness of Ti-45Al-7Nb-xB alloys increased with increase of boron addition.The properties of room temperature compression showed that the ultimatecompressive strength and compressibility decreased with increase of boron addition. And the Ti-45Al-7Nb-1.0B alloy exhibited superior mechanicalproperties, with a ultimate compressive strength of2088MPa, and thecompressibility of26.89%. Scanning electron microscopy (SEM) observationindicated that the fracture mode of Ti-45Al-7Nb-xB alloys were mainly brittlefracture.Interfacial reaction was a diffusional reaction and did not proceed evenly withthe aid of SEM, X-ray diffraction and micro-hardness tests. The results showedthat the thicknesses of interfacial reaction layer of the Ti-46Al alloy andTi-46Al-7Nb alloy with39μm and50μm were the largest when Si was added toceramic mold shell. And the thicknesses of interfacial reaction layer of the Ti-46Alalloy and Ti-46Al-7Nb alloy were respectively8μm and9μm when Al was addedto ceramic mold shell.