As the demand for materials used at high temperatures increases, researchers are committed to finding new materials that can be used at temperatures higher than the limit temperature of nickel-based alloys. Chromium (Cr) and its alloys are caused by its high melting point, good oxidation resistance, low density (20% lower than most nickel-based superalloys) and high thermal conductivity (2-4 times higher than most high-temperature alloys) Received widespread attention. Laser powder bed fusion (LPBF) is a widely used metal additive manufacturing process, which has been used to manufacture nickel-based alloys, cobalt-based alloys, titanium alloys, etc., but there is no report on LPBF processing pure Cr.
Researchers from Osaka University in Japan used LPBF processing technology to manufacture pure Cr for the first time, and controlled the crystal texture of pure Cr to study its high-temperature oxidation behavior. Related papers were published in Additive Manufacturing, an authoritative journal in the field of additive manufacturing, with the title “Crystallographic orientation control of pure chromium via laser powder bed fusion and improved high temperature oxidation resistance”.
Thesis “crystallographic orientation control of pure chromium via laser powder bed fusion and improved high temperature oxidation resistance”
Strong crystallographic texture
The relative density of pure Cr samples manufactured by Osaka University in Japan exceeds 90%, and the relative density increases with the increase of energy density, and the highest relative density is 95.47%. The manufactured sample is composed of pure chromium with a body-centered cubic (BCC) structure without any other phases. The relative strength of (200) texture increases with the increase of energy density. Under the manufacturing conditions with higher energy density, a strong crystallographic texture with (100) orientation along the structural direction (LPBF-(100) for short) is formed, and random orientation is formed when manufacturing at lower energy density The crystallographic texture (LPBF-R for short) indicates that the crystal texture of the Cr sample can be controlled by controlling the laser energy.
SEM micrographs of the yz section of the processed LPBF sample (a) E3 (LPBF-R) and (b) E6 (LPBF-(100)), and (c) XRD of pure Cr powder and processed sample result
The study found that compared with randomly oriented Cr samples, the oxide layer thickness of (100) oriented Cr samples is smaller. This is due to two factors: (1) the orientation dependence of the oxidation resistance in the grain is suppressed in the (100) crystal orientation; (2) the intergranularity caused by the special grain boundary of oxidation resistance (CSL grain boundary) Delayed oxidation. The oxide layer thickness curve conforms to the parabolic rate law. Compared with randomly oriented Cr, (100) oriented Cr has a lower parabolic rate constant. This indicates that (100)-oriented Cr is more resistant to oxidation.
(Ad) IPF diagrams of texture changes caused by different laser energy densities; (a’-d’) corresponding grain boundary diagrams; (a”-d”) yz plane {100} pole diagrams of pure Cr produced by LPBF.
(A,a’) SEM image and EPMA image of the cross section of LPBF-(100) after oxidation; (b,b’) SEM image and EPMA image of the cross section of LPBF-R after oxidation
(A) Three-dimensional micrograph of ordinary pure Cr surface before oxidation; (b) Oxide layer thickness
(A) The relationship between the quality of LPBF-(100) and LPBF-R and the square root of oxidation time;
(B) The relationship between the thickness of the oxide layer and the square root of the oxidation time
In general, studies have shown that high-temperature oxidation resistance is largely due to grain boundary density and crystallographic texture. The use of LPBF for manufacturing is conducive to controlling the crystal texture and grain boundary conditions of metal materials to obtain better oxidation resistance. Therefore, this method is expected to be used in the production of high-temperature oxidation-resistant parts for industrial use. However, the development of dense parts suitable for advanced applications still requires further research.
(Editor in charge: admin)
0 Comments for “Laser powder bed melting 3D printing controls the crystal orientation of pure chromium and improves its high temperature oxidation resistance”