Effect of Heat Treatment on Niobium Segregation of Laser-Cladded IN718 Alloy Coating
- PDF / 1,388,360 Bytes
- 9 Pages / 593.972 x 792 pts Page_size
- 100 Downloads / 217 Views
INTRODUCTION
IN718 alloy is widely used in elevated temperature applications, such as gas turbine and power generation. In IN718 alloy, niobium is an insoluble alloying element with relatively lower elastic modulus, melting temperature, and density, as well as larger atom dimension.[1] It improves the physical and chemical properties of the Ni-based alloy because the formation of topological close-packed (TCP) and geometrically closed-packed (GCP) phases contained niobium, such as c¢¢ (Ni3Nb), d (Ni3Nb), and fine carbide (MC).[1–3] However, massive or coarse Laves precipitating adjacent to the grain boundaries, formed in the welds and castings because of Nb segregation,[3–6] will significantly weaken the mechanical properties of the alloy. Moreover, the microstructure adjoined to the brittle phases can initiate microcrack preferentially and lead to initial fracture under the action of tensile stress or residual stress.[6–8] It is reported that formation of Laves consumed large amounts of niobium, resulting in weakening of matrix and decreasing of concentration of c¢¢ in the standard heat treatment.[9–11] But the effect of Nb segregation and distribution on the strengthening in the heat treatment was seldom discussed in the previous literature.[12] In this study, an IN718 alloy coating was prepared by highYAOCHENG ZHANG, Ph.D. Candidate, PULIN NIE, Assistant Researcher, and ZHUGUO LI, Professor, are with the Department of Shanghai Key Laboratory of Materials Laser Processing and Modification, School of Materials Science and Engineering, Shanghai Jiao Tong University, Shanghai 200240, P.R. China. Contact e-mail: [email protected] YIXIONG WU, Professor, is with the Department of Shanghai Key Laboratory of Materials Laser Processing and Modification, School of Materials Science and Engineering, and also with the State Key Laboratory of Metal Matrix Composites, School of Materials Science and Engineering, Shanghai Jiao Tong University. Manuscript submitted February 11, 2012. Article published online October 23, 2012 708—VOLUME 44A, FEBRUARY 2013
power diode laser cladding. 980STA standard heat treatment and direct aging (DA) were employed in the coating. The Nb segregation and distribution were investigated by microstructure observation and energydispersive X-ray spectroscopy analysis on precipitations of the laser-cladded IN718 alloy coating before and after heat treatment.
II.
EXPERIMENTAL PROCEDURES
The coatings were fabricated by a 3.5-kW Rofin DL-035Q diode laser cladding system equipped with a coaxial powder feeder nozzle. Pure argon (99.99 pct purity) was used to deliver the spherical powder to the molten pool and to prevent the molten pool from oxidation and contamination. The chemical composition of powder, produced by plasma rotation electrode process without a pore (as shown in Figure 1), is listed in Table I. The as-deposited coating is fabricated with 10 layers and 6 passes in each layer, and the dimension of the coating was 50 mm 9 10 mm 9 8 mm (length 9 width 9 height). The laser cladding processing paramet
Data Loading...
