Forming process and microwave post-treatment of WC-12 Co cemented carbide cylindrical-shaped inner structure structure by selective laser melting
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摘要: 首先采用了SLM不同扫描策略制备了WC-12Co硬质合金试样，研究了扫描策略对成形试样的影响规律，优化出最佳成形工艺。使用优化后的参数成形了圆柱形内部结构试样并进行微波后处理，分析微波后处理工艺对试样相对密度、维氏硬度和形状精度的影响规律。结果表明，最适用于打印WC-12Co硬质合金是棋盘格扫描策略，在成形能力、相对密度、维氏硬度和组织均匀性方面均优于其他扫描策略，调整扫描间距为30 μm后，试样相对密度达到最高91.6%，维氏硬度则达到
1324 HV，且棋盘格扫描策略成形圆柱形内部结构的精度也更佳；当微波热处理升温速率为40 ℃/min、温度为1300 ℃、保温时间为20 min时，试样微观缺陷数量与热处理前相比大幅减少，材料相对密度与维氏硬度显著提高，但热处理会导致部分WC晶粒尺寸增大，此时试样相对密度达到96.1%，维氏硬度达到1435 HV，且热处理后圆柱形内部结构试样的精度没有被破坏。Abstract: Firstly, different scanning strategies of SLM were used to prepare WC-12Co cemented carbide specimens, and the influence of scanning strategies on the formed specimens was investigated to optimize the best forming process. The optimized parameters were used to form the specimens with cylindrical-shaped inner structure and microwave post-treatment, to analyze the influence of microwave post-treatment process on the relative density, Vickers hardness and shape accuracy of the specimen. The results show that the most suitable for printing WC-12Co cemented carbide is the checkerboard scanning strategy, which is better than other scanning strategies in terms of forming ability, relative density, Vickers hardness and tissue uniformity. After adjusting the scanning spacing to 30 μm, the relative density of the specimen reaches the highest 91.6%, and the Vickers hardness is up to1324 HV, and the checkerboard scanning strategy has a better precision of forming the cylindrical-shaped inner structure; when the microwave heat treatment heat treatment rate is 40 ℃/min, the temperature is1300 ℃ and the holding time is 20 min, the number of microscopic defects of the specimen is greatly reduced compared with that before heat treatment, and the relative density, Vickers hardness of the material are significantly improved, but some of the WC grain sizes increase because of heat treatment, at this time, the relative density of the specimen reaches 96.1%, and the Vickers hardness reaches1435 HV, and the precision of the specimen of cylindrical-shaped inner structure is not destroyed after the heat treatment. -
图 1 WC-12 Co粉末：(a) 原始形貌；(b) 粒度分布
Figure 1. WC-12 Co powder: (a) original morphology; (b) particle size distribution
图 2 扫描策略：(a) S形；(b) 回形；(c) 棋盘格
Figure 2. scanning strategies: (a) S-shape scanning; (b) spiral scanning;(c) checkerboard scanning.
图 4 不同扫描策略WC-12 Co硬质合金试样相对密度对比
Figure 4. Comparison of relative density of WC-12 Co cemented carbide specimens under different scanning strategies
图 5 不同扫描策略下WC-12 Co硬质合金试样表面微观组织和WC晶粒尺寸分布图：(a) 棋盘格；(b) S形；(c) 棋盘格晶粒尺寸分布图；(d) S形晶粒尺寸分布图
Figure 5. Microstructure and WC grain size distribution of the surface of the WC-12 Co cemented carbide specimens under different scanning strategies: (a) checkerboard scanning; (b) S-shape scanning; (c) grain size distribution of checkerboard; (d) grain size distribution of S-shape
图 6 SLM成形过程中能量传递示意图
Figure 6. Schematic diagram of energy transfer in SLM molding process
图 7 不同扫描间距下WC-12 Co硬质合金试样相对密度与维氏硬度
Figure 7. Relative density and Vickers hardness of WC-12 Co cemented carbide specimens at different scanning spacing
图 10 悬垂圆孔与竖直圆孔形貌对比：(a) 悬垂圆孔；(b) 竖直圆孔
Figure 10. Comparison of morphology of overhanging and vertical circular holes: (a) overhanging circular holes; (b) vertical circular holes
图 12 不同扫描策略成形圆柱形内部结构对比：(a) 棋盘格扫描策略成形的Φ6悬垂圆孔；(b) S形扫描策略成形的Φ6悬垂圆孔；(c) 棋盘格扫描策略成形的Φ6竖直圆孔；(d) S形扫描策略成形的Φ6竖直圆孔
Figure 12. Comparison of the structure of holes formed by different scanning strategies: (a) Φ6 overhanging circular hole shaped by checkerboard scanning strategy; (b) Φ6 overhanging circular hole shaped by S scanning strategy；(c) Φ6 vertical hole shaped by the checkerboard scanning strategy; (d) Φ6 vertical hole shaped by the S-shape scanning strategy
图 13 不同扫描策略成形悬垂圆孔最大塌陷量与圆度测量结果：(a) 最大塌陷量；(b) 圆度
Figure 13. Maximum collapse and roundness measurements of overhanging circular holes formed by different scanning strategies: (a) maximum collapse volume; (b) roundness
图 14 热处理后WC-12 Co硬质合金试样的相对密度与维氏硬度：(a) 不同温度；(b) 不同保温时间
Figure 14. Relative density and Vickers hardness of WC-12 Co cemented carbide specimens after heat treatment: (a) different temperatures;(b) different holding time
图 15 不同温度热处理后WC-12 Co硬质合金试样表面微观组织和WC晶粒尺寸分布图：(a)
1300 ℃热处理后微观组织；(b)1400 ℃热处理后微观组织；(c)1300 ℃热处理后晶粒分布；(d)1400 ℃热处理后晶粒分布Figure 15. Microstructure and WC grain size distribution on the surface of the WC-12 Co cemented carbide specimens after heat treatment at different temperatures: (a) microstructure after heat treatment at
1300 °C; (b) microstructure after heat treatment at1400 °C; (c) grain size distribution after heat treatment at1300 °C; (d) grain size distribution after heat treatment at1400 °C
图 16 热处理前后WC-12 Co硬质合金试样表面微观组织和Co元素分布：(a)热处理前微观组织；(b)热处理前Co元素分布；(c)热处理后微观组织；(d)热处理后Co元素分布
Figure 16. Microstructure and Co element distribution on the WC-12 Co cemented carbide specimens surface before and after heat treatment: (a) microstructure before heat treatment; (b) Co element distribution before heat treatment; (c) microstructure after heat treatment; (d) Co element distribution after heat treatment
图 17 热处理前后圆柱形内部结构对比：(a) 热处理前Φ6悬垂圆孔；(b) 热处理后Φ6悬垂圆孔；(c) 热处理前Φ6竖直圆孔；(d) 热处理后Φ6竖直圆孔
Figure 17. Comparison of the structure of round holes before and after heat treatment:(a) Φ6 overhanging round hole before heat treatment; (b) Φ6 overhanging round hole after heat treatment; (c) Φ6 vertical round hole before heat treatment; (d) Φ6 vertical round hole after heat treatment
表 1 WC-12 Co粉末化学成分
Table 1. WC-12 Co powder chemical composition
Element Fe Co Ct Cf O W Mass fraction/% 0.015% 11.92% 5.38% 0.06% 0.03% Bal. 
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表 2 WC-12 Co粉末物理性能
Table 2. WC-12 Co powder physical properties
Testing Program Test results Particle size distribution/μm D10 23.68 D50 35.39 D90 49.42 Bulk density/(g·cm-3) 4.64 Flowability(s/50 g) 13.6
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表 3 预实验工艺参数
Table 3. Pre-experimentation process parameters
Laser power p/W Scanning speed v/(mm·s−1) Thickness h/mm Scanning spacing l/mm 100 390 0.04 0.03~0.07
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表 4 圆柱形内部结构成形参数
Table 4. Forming parameters for cylindrical-shaped inner structures
Scanning Strategy Scanning spacing
l /mmDiameter of the
round hole /mmChessboard 0.03 2、4、6、8 S 0.06 2、4、6、8
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表 5 热处理实验参数表
Table 5. Heat treatment experiment parameter table
Heating rate/
(℃·min-1)Heat treatment
temperature/℃Holding
time/min40 1250 10 40 1300 10 40 1350 10 40 1400 10 40 1300 20 40 1300 30 40 1300 40
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