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Streszczenie:
Although intensively researched in the last decade, additive manufacturing techniques are still subject to certain shortcomings, such as internal porosity or anisotropy of properties. In this work, we investigate the effects of postprocessing via hot isostatic pressing (HIP) on the properties of the titanium alloy Ti6Al4V produced via two various additive manufacturing methods: laser powder bed fusion (LPBF) and cold spray (CS). The LPBF produced a microstructure composed of a mixture of hcp-structured α(Ti) and α’(Ti), whereas α(Ti) and bcc-structured β(Ti) were recognized in the CS-ed materials. The subsequent HIP treatment did not cause reformation of the LPBF microstructure. This process had a significant effect on the densification of the CS-ed samples. To study the anisotropy of the material properties, the tensile and compressive strengths of the materials were determined in the planes parallel and perpendicular to the building (LPBF) and spraying (CS) directions. The LPBF materials exhibited significantly better mechanical properties stemming from the typical α/α’ martensitic microstructure, whereas the CS-ed materials presented a high number of pores and smooth and textured regions composed of recrystallized grains and grains with a high number of dislocations, respectively. The HIP treatment led to a reduction in porosity, causing a significant increase in the mechanical properties (UTS by 132%) and a reduction in the UTS anisotropy in the CS-ed materials

Słowa kluczowe:
Ti6Al4V, Laser powder bed fusion, Cold spray, Hot isostatic pressing, Mechanical properties

Streszczenie:
Degradation of power engineering steel structures requires constant monitoring of their mechanical properties to estimate remaining service life. Therefore, the current study aimed to develop a methodology that will enable for accurate determination of changes in mechanical properties of 10CrMo9-10 steel after long-term exploitation involving the Small Punch Test (SPT). Firstly, the as-received 10CrMo9-10 steel was annealed at 770 ◦C for different periods (1.5, 6 and 24 h) to deteriorate its strength to a level similar to its exploited counterpart. Then, mechanical properties were characterized by uniaxial tensile tests and the SPT method using miniaturized discs with a diameter of 8 mm and a thickness of 0.5 mm as recommended by the EN 10371:2021 standard. It allowed to determine a formula correlating the SPT results (i.e., elastic–plastic transition force and maximum force) with the yield and ultimate tensile strength. The βRp0.2 and βRm correlation factors were equal to 0.437 and 0.255, respectively. Finally, the exploited 10CrMo9-10 steel was tested by the SPT method. Based on the SPT results, the values of Rp0.2 = 236 } 27 MPa and Rm = 459 } 17 MPa were estimated, which were close to those assessed during the uniaxial tensile tests (Rp0.2 = 218 } 3 MPa and Rm = 454 } 4 MPa). It was shown that the application of such a relatively simple method is a promising way for determining the changes in mechanical properties of structural steels after long-term service at elevated temperature

Słowa kluczowe:
10CrMo9-10 steel, small punch test, mechanical properties, degradation