*3.4. Effects of Heat Treatment on Joint Tensile Properties*

After heat treatment at 700 ◦C, 750 ◦C, 800 ◦C, 850 ◦C, and 900 ◦C, the tensile strength (бb) of the Ti3Al LFW joints at room temperature was 960 ± 6 MPa, 939 ± 7 MPa, 923 ± 10 MPa, 918 ± 9 MPa, and 901 ± 9 MPa, respectively, and tensile strength (бb) of joints decreased with the temperature of heat treatment from 700 ◦C to 900 ◦C, as show in Figure 11. All fractures occurred in the BM zone of Ti3Al and there was a certain bottleneck shrinking of about 10%. As it can be seen in Figure 12, the macro-fracture was a typical cup-shaped fracture and was composed of a fibrous zone and a shear lip zone. The shear lip zone was more apparent, while the fibrous area exhibited a shallow dimple shape. After being subjected to heat treatment, the microhardness of the WZ and the TMAZ of the Ti3Al LFW joint was higher than that of the base metal, which was one of the reasons for the tensile fracture at the base metal region at room temperature.

**Figure 11.** Tensile strength results with heat treatment from 700 ◦C to 900 ◦C.

**Figure 12.** Tensile fracture morphology of the Ti3Al LFW joint at room temperature.
