真空燒結和熱均壓以及熱處理對於TaC強化鈷基超合金微觀組織與機械性質之影響

The Effects of Vacuum Sintering, HIP and Heat Treatments on the Microstructure and Mechanical Properties of Co-based Superalloys Strengthened with TaC Particles.

陳健中(Chien Chung Chen)

指導教授 ： 張世賢

國立臺北科技大學/工程學院/材料科學與工程研究所/碩士(2013年)

https://doi.org/10.6841/NTUT.2013.00719

摘要

鈷基超合金具有良好的抗熱腐蝕性、抗氧化性、抗疲勞以及優越的高溫強度，它們被廣泛地應用在航太引擎中的噴嘴導向葉片和渦輪葉片，鈷基超合金通常利用碳化物析出(例如M6C與M23C6)和固溶處理來產生強化效果。金屬基複合材料已知具有相當硬及展現良好的耐磨特性，而在鈷基超合金中，最常被用到的碳化物是鉭比鉻，鉭比鉻是更有效率的碳化物形成元素，也因此更容易在富鉻相(Cr-rich)的鈷基合金中發現。
本研究主要是將鈷基超合金粉末添加TaC微粉，其添加量分別是10、15與20 wt%，粉末的混合是經由球磨加以完成；此外，將原始鈷基超合金與三種配比混合的粉末以1260、1270、1280與1290°C進行真空燒結，接著再進行一系列的熱均壓和熱處理。熱均壓處理參數為1250°C 125 MPa 100分鐘；而固溶熱處理是在1100°C持溫40分鐘後，淬火冷卻，並在850°C進行時效，時效時間分別是9、12與15小時，最後以視孔隙率、硬度試驗、三點抗彎強度(TRS)試驗、OM與SEM顯微組織觀察等進行分析。
由實驗結果顯示，1290°C燒結之試片產生熔化現象，而在三點抗彎強度方面，最高的TRS是添加10 wt% TaC的合金在1270°C燒結之後，接著進行熱均壓處理和時效處理12小時，其TRS值可達到1812.4 MPa。此外，在提高鈷基合金的機械性能方面，碳化鉭粉末的添加量發揮重要的作用；其硬度值相對的有所提升，從72.5 HRA 提高至 80.1 HRA。另一方面，最高的硬度是添加20 wt% TaC的鈷基合金，在經過1270°C燒結再施以熱均壓處理及15小時時效後，具有最高的硬度82.8 HRA。在微觀組織方面，原始鈷基超合金經時效處理後，在基地中同時析出了M6C還有M23C6 的碳化物。而在添加了碳化坦的合金中，經時效12小時後，具有更均勻的M6C、M23C6和MC碳化物析出在基地和晶界中，可以明顯地改善其機械性質；然而，經過時效15小時處理後，鈷基合金會有過時效的現象產生，進而造成機械性質降低。

關鍵字

鈷基超合金 ； 金屬基複合材料 ； 碳化鉭 ； 真空燒結 ； 熱均壓

並列摘要

Cobalt-based superalloys have good hot-corrosion resistance, antioxidation, fatigue properties and excellent high-temperature strength. They are widely used in manufacturing nozzle guide vanes and turbine blades in aerospace turbine engines. Cobalt-based superalloys are usually strengthened by precipitated carbides (such as M6C and M23C6) and solid-solution. Metal matrix composites (MMC) are known to be very hard and to exhibit exceptional wear resistance. Among them, the most used in alloys is TaC carbide, notably in cobalt-based superalloys. Tantalum is a carbide former element which is more efficient than chromium. Therefore, TaC carbides can be easily obtained in Cr-rich cobalt alloys.
In this study, we mixed and added different amounts of TaC powders (10, 15 and 20 wt%) to the cobalt-based superalloy powders. The mixing process was finished by ball milling. In addition, the original cobalt-based powders and mixing powders (cobalt-based added TaC) were sintered at 1260, 1270, 1280 and 1290°C, and then, a series of HIP processes and heat treatments were performed. The parameters of the HIP treatment were 1250°C, 125 MPa and 100 min. The solid-solution heat treatment processes involved heating to 1100°C for 40 min for quenching and then, aging at an 850°C holding for 9, 12 and 15 h, respectively. Various material characterization techniques were used to evaluate the materials’ properties and microstructures including apparent porosity, hardness test, transverse rupture strength (TRS) test and OM and SEM microstructural examinations.
The experimental results showed that the sintering specimens generated a melting phenomenon at 1290°C. Furthermore, the highest TRS value of 1812.4 MPa was obtained by the 10 wt% TaC additive powder, which was sintered at 1270°C followed by the HIP process and aging treatment for 12 h. Moreover, the added amounts of TaC powder played an important role in improving the mechanical properties of a cobalt-based alloy. It was proven that the hardness was from 72.5 HRA to 80.1 HRA. In addition, the highest hardness value of 82.8 HRA was obtained by the 20 wt% TaC additive powder, which was sintered at 1270°C followed by the HIP process and aging treatment for 15 h. From the microstructural observations, both M6C and M23C6 carbides precipitated in the matrix of the Co-based superalloy after the aging treatment. However, the more uniform precipitations of M6C, M23C6 and MC carbides precipitated in the matrix of the Co-based superalloy added TaC powders after aging treatment for 12 h. This could effectively improve the mechanical properties of the alloys. Conversely, the over aging phenomenon appeared after aging treatment for 15 h, which resulted in decreased mechanical properties.

並列關鍵字

Cobalt-based superalloys ； MMC ； TaC ； Vacuum Sintering ； HIP

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