Study Of Prepare And Microstructure And Mechanical Properties On Laminated TiB₂-TiAl Composite Sheet

TiAl alloy is acknowledged as the one of the most promising new materials inrecent times, but the pronounced brittleness at room temperature will seriously affectthe application and process of titanium aluminium alloy. In my research I choose Almatrix composite foils and Ti elemental foils as raw materials, and TiB₂-TiAl compositesheet was prepared by bonding rolling and reactive annealing. In this paper, theprocesses of phase transition in the process of reactive annealing were studied by usingoptical microscope （OM）, scanning electron microscopy （SEM）, X-ray diffraction（XRD） method. The mechanical properties of material at room temperature and hightemperature were tested。To increase the density of material, we need estimate the volume fraction of TiB₂particles to realize the structure of TiB₂-rich layers like pearls. TiB₂/Al composite foilsand Ti foils were stacked alternately, and then put them into the pack to prepare theTi/Al sheet combined with strong interface by hot rolling directly. To simplify thepreparation process, Ti-（TiB₂/Al） composite sheet was processed by reactive annealingdirectly at high temperature. The composite sheet was packed to prevent the loss ofaluminium. To research a variety of high temperature reaction annealing temperatureand holding time, and then this paper proved that1300C/30min was the optimum heattreatment process. The hot-press sintering was treated by1300C/2h/40MPa fordensifying treatment. The composite sheet was processed by homogenization treatment,and then the material just left the stability intermetallic compounds of Ti3Al and TiAl.Through the laminarization treatment，eventually the material producted γ-TiAl phasewith fully lamellar and a small amount of equiaxed γ-TiAl phase, and TiB₂particlesgathered with string structure in fully lamellar γ-TiAl phase.The fracture toughness with parallel and perpendicular to the rolling direction of thismaterial were9.08±0.24MPa·m^1/2and11.12±0.54MPa·m^1/2. The tramslamellar fracturewas the main fracture mode. Elastic modulus of the room temperature tensile test was170.38GPa. Mechanism of fracture was brittle fracture. High temperature tensile testwas tested for this composite sheet，the tensile strength reached320MPa at750C, andthe elongation reached4.81%. With the increase of tensile test temperature, theelongation of composite sheet increased. The elongation reached nearly7%at900C,but the material’s elastic modulus was not well. The translamellar fracture is the main fracture mode for the high temperature tensile fracture mode. High temperaturecompression test was carried out on the sheet. The compressive performance showedobvious anisotropy, and under the condition of1100C/0.001s^-1its flow stress reached124.16MPa at the direction of perpendicular to the rolling, and from macro observationdifferent loading direction had different crack propagation method.