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生长温度是指生长ZnSe晶体基板的温度,根据物理气相沉积的工艺原理,此温度为影响ZnSe晶体质量的关键因素。为了研究生长温度对PVDZnSe晶体尺寸的影响,选择920、960、1 000 ℃三个生长温度来进行样品沉积。图1是利用金相显微镜观察到的在三个不同生长温度下所制备样品的表面形貌,可以看出三种样品的晶粒尺寸存在明显差异。生长温度为920、960、1 000 ℃的ZnSe晶粒尺寸分别约为20~180、300~2 000、1 200~2 800 μm。可见随着生长温度的升高,PVDZnSe材料的晶粒尺寸也在变大。这是因为,随着生长温度的升高,粉体原料的蒸发速率增加,晶核在沉积基板上可以接触到更多的气体分子,从而加快了晶体生长速率。同时,晶粒还会将周围的小晶粒进行吞,即发生二次结晶现象。生长温度越高,晶粒的二次结晶现象就越明显。因此,ZnSe晶体材料的晶体尺寸随着沉积温度的增加而快速增大。生长温度越低得到的PVDZnSe材料晶粒尺寸越小。理论上讲,小晶粒尺寸利于优化ZnSe材料的可加工性。为了表征所制备材料的可加工性能,对材料的断裂韧性与硬度进行了测试,并根据测试数据对其脆性指数进行了计算。表1为不同温度条件下制备的PVDZnSe材料的可加工性数据情况,其中920 ℃条件下制备的PVDZnSe由于厚度较小,无法进行断裂韧性测试。从表1中可以看出,随着晶粒尺寸的增加,材料的硬度在缓慢增加,断裂韧性逐渐降低,所以其脆性指数在逐渐增加,可加工性能变差。
图 1 不同温度条件下制备的PVDZnSe材料的表面形貌图
Figure 1. Surface morphology of PVDZnSe prepared at different temperatures
表 1 不同温度条件下制备的PVDZnSe材料的可加工性相关数据
Table 1. Machinability data of PVDZnSe materials prepared at different temperatures
No. T/ ℃ Grain size/μm HV/GPa KIC/MPa·m1/2 HV/KIC/μm−1/2 1 920 20 -180 0.93 - - 2 960 300-2000 1.02 0.63 1.62 3 1000 1200-2800 1.07 0.46 2.32 但实验过程中发现,当生长温度为920、960、1 000 ℃时,PVDZnSe晶粒的生长速率分别为0.1、0.5、0.6 mm/h,即PVDZnSe生长速率会随着生长温度的降低而显著减慢。生长速率过于缓慢会延长晶体生长周期,导致生产成本增加,并且在长时间生长条件下,晶粒也会慢慢长大,0.5 mm/h被认为是最佳的生长速度。因此,从晶粒尺寸与生长速度两方面综合考虑,960 ℃为PVDZnSe的最佳生长温度。
对上述三种PVDZnSe材料进行光学性能测试,测试结果如图2所示。在2~14 μm波长范围内,三种材料的平均透光率分别为70.1%、70.3%、70.2%。说明晶粒尺寸对PVDZnSe材料在2~14 μm波段范围内的光学透过率基本没有影响。
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ZnSe的原料特性会影响其蒸发速率,而蒸发速率又会影响PVDZnSe材料的晶体生长过程进而影响材料的晶粒尺寸。对比分析相同沉积工艺条件下由不同ZnSe粉体原料制备的PVDZnSe材料的微观形貌。所选三种原料分别标记为Ⅰ、Ⅱ、Ⅲ,原料Ⅰ和Ⅱ为粉体原料,原料Ⅲ为块体材料。采用场发射扫描电子显微镜测得三种原料的微观形貌如图3所示。原料Ⅰ和原料II的微观形貌图放大倍数为5000×,是采用场发射扫描电子显微镜在5000×放大条件下获得。原料III为采用金相电子显微镜在50×放大条件下获得。从图3可以看出原料Ⅰ、Ⅱ、Ⅲ的晶粒尺寸范围分别为2~10 μm、10~20 μm和300~2 000 μm。
图4为所选三种原料的X射线衍射图。三种原料都在相同的位置出现衍射峰,与ZnSe的JCPDS 卡片库中PDF#37-1463标准卡片的特征峰位完全吻合。三种原料的晶粒尺寸尽管不同,但是均为微米级别,所以三种原料的XRD图谱均未出现宽化现象,峰型十分相似。
图 4 选用三种原料(I、II和III)的X射线衍射图
Figure 4. X-ray diffraction patterns of the three raw materials (I, II and III)
图5为利用金相显微镜观察到的三种原料在生长温度为960 ℃条件下制备出的PVDZnSe晶体材料的表面形貌图。从图中可以看出,采用Ⅰ、Ⅱ和Ⅲ三种原料制备得到PVDZnSe晶体材料的粒径分别为200~1 500 μm,300~2 000 μm以及880~2 500 μm。PVDZnSe晶体材料的粒径随着原料粒径的增加而呈现增加的趋势。这是因为,在相同温度下,原料粒径尺寸越大就越难蒸发,使得ZnSe气体分子在沉积基板上的生长速率远大于成核速率,沉积基板上的ZnSe晶核快速长大,从而导致晶粒尺寸偏大。图6为三种原料在室温至1200 ℃范围内的热重曲线。从图中可以看出,在760~820 ℃之间,三种原料的失重程度为原料Ⅰ>原料Ⅱ>原料Ⅲ。在820~940 ℃范围内,原料Ⅰ失重程度最大,原料Ⅱ和原料Ⅲ程度相近。在940~1 200 ℃之间,原料失重程度为原料Ⅰ>原料Ⅱ>原料Ⅲ。因此,可以推测出,当生长温度为960 ℃时,原料Ⅰ的蒸发速率最快,原料Ⅱ次之,原料Ⅲ最慢。这也解释了在相同制备工艺条件下,由原料Ⅰ制备的PVDZnSe晶粒尺寸最小的原因。
图 5 分别采用三种原料在相同工艺条件下制得的PVDZnSe材料的表面形貌
Figure 5. Surface morphology of PVDZnSe materials from three kinds of raw materials respectively under the same process
图 6 三种ZnSe原料在室温至1200 ℃温度范围内的热重曲线
Figure 6. Thermogravimetric curves of the three kinds of ZnSe raw materials in the temperature range from room temperature to 1 200 ℃
表2为采用不同原料在相同生长条件下制备的PVDZnSe材料的可加工性数据情况,从表2中很容易可以看出,随着晶粒尺寸的增加,材料的硬度也在缓慢增加,断裂韧性逐渐降低,因此脆性指数增加,可加工性能变差。
表 2 三种原料制备的PVDZnSe材料的可加工性数据
Table 2. Machinability data of PVDZnSe materials prepared with three kinds of raw materials
No. Raw material Grain size/
μmHV/
GPaKIC/
MPa·m1/2HV/
KIC/μm−1/21 Ⅰ 200-1500 0.98 0.66 1.48 2 Ⅱ 300-2000 1.02 0.63 1.62 3 Ⅲ 880-2500 1.04 0.61 1.70 图7为三种材料的透过率曲线值。采用原料Ⅰ、原料Ⅱ和原料Ⅲ 制备的PVDZnSe材料的透过率分别为70.1%、70.3%、70.3%。可见原料尺寸对PVDZnSe的透过率影响不大。
图 7 相同工艺条件下由三种原料制备的PVDZnSe样品光学性能
Figure 7. Optical properties of PVDZnSe prepared with three kinds of raw materials under the same process
由PVDZnSe材料加工得到的光学零件实物样件如图8所示。
Study of preparation process of PVDZnSe infrared optical materials based on different grain sizes
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摘要: ZnSe以其优异的光学性能与机械性能,一直是光学零件的首选材料之一。光学窗口、光学透镜等光学零件的制作成本很大程度上取决于光学材料的可加工性,加工成本占制作总成本的50%以上。从微观结构上来看,光学晶体材料的可加工性又与晶粒尺寸相关。文中采用物理气相沉积(PVD)法制备了PVDZnSe红外光学材料,并从沉积温度与原料性能两个方面研究了PVDZnSe制备工艺对其晶粒尺寸和可加工性的影响。研究表明:在920、960、1 000 ℃三个温度条件下,随着沉积温度升高,PVDZnSe材料晶粒呈现增加的趋势,其尺寸范围分别为20~180 μm、300~2000 μm和1 200~2 800 μm。在相同工艺参数条件下,选用粒径分别为2~10 μm、10~20 μm和300~2 000 μm的三种ZnSe原料制备PVDZnSe。随着原料ZnSe晶粒尺寸的增加,所得PVDZnSe的晶粒尺寸显著增大。结果表明,随着晶粒尺寸增加,脆性指数也相应增加,即PVDZnSe可加工性能在逐渐变差。研究还发现,在一定的晶粒尺寸范围内,材料的透过率差别不大,在2~14 μm波长范围内,PVDZnSe材料的平均透过率均能达到70%以上。该研究为PVDZnSe材料在光学零件领域的应用提供了实践经验和有力的技术支撑。Abstract: ZnSe has always been one of the preferred materials for optical parts due to its excellent optical and mechanical properties. The manufacturing cost of optical parts such as optical windows and optical lenses largely depends on the machinability of optical materials, and processing costs account for more than 50% of the total manufacturing costs. The machinability of optical materials is related to the grain size. In this paper, the physical vapour deposition (PVD) method was employed to prepare PVDZnSe infrared optical materials, and the influence of the PVDZnSe preparation process on its grain size and machinability was investigated from the aspects of deposition temperature and raw material properties. It was demonstrated that under the three temperature conditions of 920 ℃, 960 ℃ and 1000 ℃, with the higher deposition temperature, the grain size of the PVDZnSe material showed an increasing trend, and the size ranges were 20-180 μm, 300-2000 μm and 1200-2800 μm, respectively. Under the same process parameters, the PVDZnSe materials were prepared from three different ZnSe raw materials with particle diameters of 2 -10 μm, 10-20 μm and 300-2000 μm. With the increase in grain size of the ZnSe raw materials, the grain size also increased. The results show that the grain size of the obtained PVDZnSe increases significantly, and the brittleness index also increases, which indicates that the machinability of PVDZnSe gradually worsens. The study also found that the influence of grain size on the transmittance of the PVDZnSe material is not significant. The average transmittance of the PVDZnSe material can reach more than 70% in the wavelength range of 2-14 μm. This study provides practical experience and technical support for the application of PVDZnSe optical parts.
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Key words:
- PVDZnSe /
- grain size /
- deposition temperature /
- raw material
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表 1 不同温度条件下制备的PVDZnSe材料的可加工性相关数据
Table 1. Machinability data of PVDZnSe materials prepared at different temperatures
No. T/ ℃ Grain size/μm HV/GPa KIC/MPa·m1/2 HV/KIC/μm−1/2 1 920 20 -180 0.93 - - 2 960 300-2000 1.02 0.63 1.62 3 1000 1200-2800 1.07 0.46 2.32 表 2 三种原料制备的PVDZnSe材料的可加工性数据
Table 2. Machinability data of PVDZnSe materials prepared with three kinds of raw materials
No. Raw material Grain size/
μmHV/
GPaKIC/
MPa·m1/2HV/
KIC/μm−1/21 Ⅰ 200-1500 0.98 0.66 1.48 2 Ⅱ 300-2000 1.02 0.63 1.62 3 Ⅲ 880-2500 1.04 0.61 1.70 -
[1] Wang Y T, Sun H Q, Guo Z Y, et al. Structures and thermodynamic properties of ZnSe [J]. Journal of Function Material, 2010, 41(3): 481-483,487. [2] Wei N G, Jiang L P, Li D X, et al. Study on the defects of ZnSe polycrystalline materials prepared by chemical vapor deposition method [J]. Journal of Synthetic Crystals, 2020, 49(1): 152-157. [3] Chen Q, Fu X H, Jia Z H, et al. Research on processing technology of ZnS crystal [J]. Journal of Changchun University of Science and Technology (Natural Science Edition), 2013, 36(3-4): 119-123. [4] Zhang W Y, Gao H. Microstructure properties and fabrication of machinable ceramics [J]. Journal of Synthetic Crystals, 2005, 34(1): 169-173. [5] Lawn B R, Marshall D B. Hardness, toughness, and brittleness: an indentation analysis [J]. J Am Ceram Soc, 1979, 62(7-8): 347-350. doi: 10.1111/j.1151-2916.1979.tb19075.x [6] Boccaccini A R. Machin ability and brittleness of glassceramics [J]. J Mat Pro Tech, 1997, 65(1-3): 304-306. [7] Yu H Z. Infrared Optical Material [M]. Beijing: National Defense Industry Press, 2007: 143, 164, 183, 252. ( in Chinese) [8] Townsend D, Field J E. Fracture toughness and hardness of zinc sulphide as a function of grain size [J]. J Mater Sci, 1990, 25(2): 1347-1352. doi: 10.1007/BF00585448 [9] Popov K B, Dimov S S, Pham D, et al. Micromilling: Material microstructure effects [J]. Proceedings of the Institution of Mechanical Engineers Part B: Journal of Engineering Manufacture, 2006, 220(11): 1807-1813. [10] Yu J F, Wu G J, Zhu L. Research progress of the infrared material zinc selenide preparation methods [J]. Guangdong Chemical Industry, 2017, 16(44): 141-142. [11] Yang Y Y, Fang Z Y, Cai Y C, et al. Growth of transparent polycrstal zinc selenide by chemical vapor deposition [J]. Journal of the Chinese Ceramic Society, 2004, 32(8): 946-949. [12] Yang H, Guo L, Wei N G. Numerical simulation of CVDZnSe gas flow pattern and experimental study on optical properties [J]. Journal of Crystal Growth, 2020, 546: 125779. [13] Wei N G, Jiang L P, Li D X, et al. A hot isostatic pressing strategy for improving the optical transmission of polycrystalline CVD ZnSe [J]. Applied Physics A, 2019, 125: 777. doi: 10.1007/s00339-019-3080-0