Preparation And High Temperature Transformation Behaviors Of The Laminated TiBw-TiAl Composites

As a kind of novel structure materials with excellent properties, the Ti Al-based alloys could replace some tradition materials in the aerospace areas including aircrafts and automotive engines with reducing weight and improving high temperature strength. However, because of the intrinsic friability, the Ti Al-based alloys are poor in forming ability, make it difficult to fabricate the Ti Al-based alloy sheets by traditional hot rolling process. In this paper, the mechanical properties of the Ti Al sheet are improved by introducing the laminated structure, as well as the Ti Bw reinforcements into the matrix. OM、SEM、TEM and EBSD was used to research the Ti Bw-Ti Al composites in the heat treatment process of phase composition, reveals the layered structure formation mechanism of Ti Bw-Ti Al composites.:Discussed the different content of lamellar Ti Al based composites reinforced with Ti Bw density and hardness changes and high temperature deformation behavior of Ti Bw-Ti Al composites, reveals the different deformation conditions and different content of Ti Bw-Ti Al based composites deformation and microstructure evolution.(Ti B/Ti)-TiAl3 laminate was obtained after low temperature annealing at 660℃/5h. Because of the different diffusion rates of Ti and Al in the reaction of annealing, Kirkendall effect existed and the Ti Al3 was porous structure. When the laminate was subsequently annealed at 1250℃/25MPa/5h, the holes in the material were observably removed. Al and Ti interdiffused constantly and then produced Ti Al and Ti3 Al. As the material composition was not uniform, the poor Al area and the rich Al area existed. With the heat treatment, the poor Al area produced fully lamellar(α2-Ti3Al/γ-Ti Al) layer and the rich Al area produced the equiaxed γ-Ti Al layer, finally the double layered structure Ti Al sheet was prepared. Ti Bw was preserved and form Ti Bw-rich laminate. The laminated Ti Bw-Ti Al composite is composed by Ti Al layer and Ti Bw-rich layer, and the Ti Al layer is composed by alternately arranged fully lamellar(α2-Ti3Al/γ-Ti Al) layer and the equiaxed γ-Ti Al layer, and the Ti Bw-rich layer was a high volume fraction of Ti B whisker aggregation layer. With Ti B whisker content increased, composite layered structure remained the same, and Ti Bw-rich layer thickness increase.When Ti Bw content to 2.2vol.%,(α2-Ti3Al/γ-Ti Al) layer average grain size is about 30μm, axis γ-Ti Al average grain size is about 8μm.Density test results show that the density of layered Ti Bw-Ti Al composites of more than 95%, The content of Ti B whisker has almost no effect to the density of the composites. The hardness of fully lamellar layer is higher than equiaxed layer and the hardness of Ti Bw-rich is highest, which means the add of the reinforcement to the matrix is beneficial to the improvement of the hareness of the matrix.Compressive deformation behavior of high temperature indicates that when the temperature is below 1110 ℃,Ti B-Ti Al composite tissue shows typically buckling deformation, through cracks were observed. As the deformation temperature increased organization tends to be uniform, crack shows shorter. When the temperature reached 1250℃, cracks disappear. Optimum process conditions for deformation temperature is 1150-1250℃, 0.001s-1.