Impact of laser process parameters in direct energy deposition on microstructure, layer characteristics, and microhardness of TC21 alloy

Abstract

In the present study, layers consisting of 40% Stellite-6 and 60% WC were deposited on Ti-6Al-3Mo-2Sn-2Zr-2Nb-1.5Cr-0.1Si (TC21) alloy by means of direct energy deposition (DED) technology aiming to improve the microstructure and microhardness. Five powder feeding rates ranging from 20 to 100 ɡ min−1 were applied using CW fiber-coupled diode laser with 4 kW output power. The deposited layers were analyzed via scanning electron microscopy (SEM), energy-dispersive X-ray analysis (EDX), and X-ray diffractometry (XRD). The results show that WC particles are dispersed in a heterogeneous manner in the deposition zone, especially at the rates 20, 40, and 60 ɡ min−1. In addition, microcracks appeared in the interface zone particularly at 100 ɡ min−1 due to the higher induced residual stresses caused by the difference in the coefficient of thermal expansion between Stellite-6, WC particles, and TC21 substrate alloy. Several complex carbides and intermetallic compounds such as W2C, TiC, Cr7C3, Co3W3C, and Co25Cr25W8C2 were detected in the deposited layers depending on the powder feeding rate. With further increase in the powder feeding rate, the fractions of W2C and the bulk (unmelted) WC particles were increased and that of the TiC particle was reduced correspondingly due to the thermal diffusion. The layer thickness increased from 1.3 to 2.7 mm when the powder feeding rate increased from 40 to 100 ɡ min−1, while the dilution ratio decreased from 23 to 5.3% as a result of the thermal diffusion of the laser energy. The microhardness of the composite was found to be three times higher than that recorded for the TC21 substrate (1020 vs. 340 HV0.05). The results revealed that the best homogeneous microstructure with the highest microhardness was achieved at the powder feeding rate of 100 ɡ min−1 whereas microcracks free layers were accomplished at 40 ɡ min−1.

Enhancing Metal Forging Tools and Moulds: Advanced Repairs and Optimisation Using Directed Energy Deposition Hybrid Manufacturing

“…The repair process for moulds encountered issues primarily linked to cracks that manifested post the DED process stage [29]. Key factors contributing to these challenges include the choice of material and the parameters of the deposition process.…”

Modeling of wear resistance for TC21 Ti-alloy using response surface methodology

“…In addition, compared to room temperature, the wear rate was reduced by 67.4-86.5% and oxidation wear mechanism was the main mechanism. Far from using traditional heat treatment processes to control wear characteristics of the TC21 alloy, a lot of research [14][15][16] reported the exploiting of surface modification technology and oxidation process to improve the hardness and wear resistance of the TC21 alloy.…”

Investigation of Microhole Quality of Nickel-Based Single Crystal Superalloy Processed by Ultrafast Laser

“…These processes are mainly related to the pulse width and pulse energy density of the femtosecond laser. This leads to significantly less damage compared to long-pulse lasers [15,16].…”