Ti65 is a new type of high-temperature titanium alloy that is designed and applied in the field of high temperature of 650 ℃. Due to its poor plasticity, Ti65 is difficult to create and process using traditional methods. Laser deposition manufacturing technology is a new processing method that has several technical advantages when it comes to the preparation of new alloys. The Ti65 titanium alloy samples used in this study were created using this technology. Due to the principle of laser deposition manufacturing, the formation of column crystals is generally unavoidable. These crystals lead to anisotropy in the microstructure and the mechanical properties of the deposited sample. Therefore, it is important to analyze the microstructure and mechanical properties of the sample in different sections and directions. We hope that our findings will be useful in the design and application of laser-deposited Ti65 alloys.

The experiment was carried out on the laser deposition manufacturing equipment at the National Defense Key Laboratory of Shenyang Aerospace University. Pure argon was used as powder feed and protective gas to prevent Ti65 from being contaminated by H and O during deposition. The forged TA15 was used as the substrate with a thickness of 30 mm. During the deposition process, the laser power was 5 kW, the spot diameter was 5 mm, the scanning speed was 10 mm/s, the powder-feeding rate was 10-20 g/min, the single layer height was 0.8 mm, and the overlap rate was 50%. In this experiment, short-edge and one-way reciprocating layer-by-layer scanning was used. The size of the deposited sample was 250 mm×15 mm×80 mm. An abrasive paper of 400-2000 mesh was used for grinding, and a polishing cloth was used on the sample for 50 min. The sample was equally divided in two by wire cutting, the first piece was annealed at 900 ℃/4 h/air cooling, while the second was kept in the as-deposited. The test blocks were cut along the XOY, YOZ, and XOZ planes by wire cutting, and the metallographic specimen was embedded and tested for microhardness. The test blocks were located in the middle of the sample. Three tensile specimens with a diameter of 5 mm and standard distance of 25 mm were cut along the XOY and XOZ planes, respectively. The tensile tests were carried out on an electronic universal testing machine, and the tensile results were averaged. The dimensions of the different phases were measured using Image J software. The microstructure and fracture morphology were observed using a GX51 optical microscope and ΣIGMA scanning electron microscope. The hardness of the specimen was tested using an HVS-1000A microhardness tester. Finally, ten values were measured on each test surface, and the average value was obtained (loading load of 1.96 N and duration of 10 s).

The macroscopic morphology of the deposited sample on distinct sections differed (Fig.2). Coarse columnar crystals and parallel-distributed layered structures were formed along the deposition direction in the laser-deposited Ti65 samples and α-lath coarsening was obvious in the layered structure. A section in the perpendicular (to the deposition) direction exhibited an equiaxed crystal structure. The microstructures on different sections were similar as they had lamellar structures (Fig.3). After annealing, the grain boundaries in different sections were intermittent, the α-lath was coarsened, the microstructure was a basketweave structure, and the anisotropy of the microstructure was not notable (Fig.4). The strengths of the as-deposited samples stretched along the deposition direction and perpendicular (to the deposition) direction were 1015 and 1055 MPa and their corresponding elongations were 11.4% and 8.4%, respectively (Table 2). After annealing, the strengths along the deposition direction and perpendicular (to the deposition) direction increased to 1025 and 1079 MPa, and the corresponding elongations increased to 12.7% and 10.5%, respectively. The fracture models of the as-deposited and annealed samples in different directions were quite disparate. The difference in macroscopic morphology led to the difference in microhardness in distinct sections. Also, the large number of equiaxed crystals contributed to the highest microhardness in the XOY section. The microhardness of the as-deposited sample along the deposition direction was slightly lower compared to the microhardness in the perpendicular (to the deposition) direction by 20 HV0.2_{(Fig.6). After annealing, the microhardness values in different directions were similar and close to 400 HV0.2.In this study, Ti65 samples were successfully created using laser deposition manufacturing method. The microstructure and mechanical properties of the as-deposited samples exhibited anisotropy. After annealing at 900 ℃/4 h/air cooling, the tensile strength, plasticity, and microhardness increased but the anisotropy was not notable.}

Annealing can change the microstructure, improve the mechanical properties and weaken the anisotropy of the comprehensive mechanical properties of laser-deposited Ti65.