固液反应法制备增强体层状分布的TiAl基复合材料板

TiAl-BASED COMPOSITE SHEET WITH MULTI-LAYER DISTRIBUTED REINFORCEMENT PREPARED BY SOLID-LIQUID REACTION

将纯Ti箔和TiB_2/Al复合材料箔交替堆垛,通过热轧获得Ti-(TiB_2/Al)叠层,随后进行热处理使固态Ti和液态TiB_2/Al快速发生化学反应,近净成形制备出增强体TiB_2颗粒呈层状分布的TiAl基复合材料板材.研究热处理过程中的相转变和组织演变规律,并测试和评价了最终层状TiB_2-TiAl复合材料板材拉伸性能.结果表明:固态Ti和液态TiB_2/Al复合材料反应首先生成多孔结构TiAl_3相,1300℃,2 h,50 MPa的压力烧结实现材料致密化,随后热处理时TiAl_3与Ti继续发生反应扩散,最终生成全层片结构(α_2-Ti_3Al+γ-TiAl)层,TiB_2不参与任何反应,且呈层状分布于基体(α_2+γ)层中.TiB_2-rich层组碍了(α_2+γ)层的全层片组织粗化,并大幅提高了层状TiB_2-TiAl复合材料板材的高温拉伸性能.

TiAl-based alloy have potential as high temperature structural materials for aerospace applications, especially for thermal protection systems in aerospace vehicles including skin materials. Unfortunately, the ductility and formability of TiAl-based alloys are rather poor and thus γ-TiAl sheets or foils are quite difficult to be manufactured by traditional methods and still far from practical applications. In the present work, commercial pure Ti foils and in-house fabricated TiB2/Al composite foils were alternately stacked and rolled to prepare Ti-（TiB2/Al） laminates, and then heat treatment was utilized to make liquid Al react with solid Ti,and finally TiAl-based composite sheet with multi-layer distributed reinforcement TiB2 particles were achieved. This method avoided the direct deformation of brittle TiAl billets and thus the near-net-shape processing of TiAl-based alloys sheets was feasible. Phase transformation and microstructure evolution during heat treatment were investigated and mechanical properties of the resulting micro-laminated TiB2-TiAl composite sheets were evaluated. The results showed that porous TiAl3 layers were produced by the reaction between liquid Al and solid Ti because of Kirkendall effect, and the following densification treatment under 50 MPa at 1300℃ for 2 h significantly improved the relative density of material. Subsequently, the reaction diffusion between TiAl3 and residual Ti proceeded in the following heat treatment, and finally fully lamellar （α2-Ti3Al＋γ-TiAl） layers were obtained. TiB2 particles did not participate in any reaction and remained, and displayed multi-layered distribution in the matrix（α2-Ti3Al＋γ-TiAl） layers. TiB2-rich layer hindered the coarsening of lamellar colony of （α2-Ti3Al＋γ-TiAl） layer. Tensile properties at 800℃ of multi-layered TiB2-TiAl composite sheets remarkably increased because of an increase of energy dissipation caused by plastic deformation.