标准超声振动气蚀孕育期内材料响应与表面形貌

材料在气蚀孕育期内仅发生极轻微的磨损，但以弹/塑性变形和晶粒拔出等方式对气蚀做出响应，具体的响应方式则随材料种类而不同.通过对孕育期内材料响应和磨损表面形貌的研究，探索不同材料响应与磨损表面形貌的关系，从而建立以表面粗糙度测量和光学显微镜观察等方式进行材料孕育期的研究.本文在标准超声振动气蚀试验机上进行了纯铜、镍基合金Hastelloy C-276和Sialon陶瓷共三种材料的气蚀试验，着重考察了它们在各自孕育期内的表面粗糙度参数（表面粗糙度R_a和核心粗糙度深度R_k）以及蚀坑面积比的变化.研究结果表明：纯铜和Hastelloy C-276在孕育期内主要以塑性变形为主.R_k不仅可以更好地反映孕育期乃至整个气蚀过程的材料表面形貌变化，还能反映不同金属在孕育期内塑性变形的程度.Sialon陶瓷在孕育期内以新蚀坑的形成为主，伴随着少量蚀坑的长大，蚀坑面积比很好地表征了陶瓷材料孕育期的变化.

Material Response and Surface Morphology in Incubation Period of a Standard Ultrasonic Vibration Cavitation Erosion Test

Materials experienced mild wear in incubation period and responded cavitation in terms of elastic/plastic deformation or grain pull-out. The way of response varied with the type of material. In order to understand the incubation period, ways of surface roughness measurements and light microscope observations have been established through the study of material response, worn surface morphology and their relationship in incubation period. The present study evaluated resistance to cavitation erosion of three materials including pure Cu, nickel-base alloy Hastelloy C-276 and Sialon ceramic using a standard ultrasonic vibratory cavitation erosion apparatus and focused on the evolution of surface roughness parameters (roughness R_a and Core roughness depth R_k) and area fraction of cavities of the three materials in their own incubation period. R_a and R_k were very sensitive to plastic deformation of pure copper and Hastelloy C-276 in the incubation period, but not always to early material removal. R_k had a similar curve with R_a in the whole process of cavitation, and its trend was more obvious. R_k was a better surface roughness parameter to reflect the surface change in incubation period and the whole cavitation process than R_a. Furthermore, it could reflect the extent of plastic deformation of different metal in incubation period. For Sialon ceramic, R_a and R_k remained nearly unchanged in the incubation period while area fraction of cavities presented an approximate linear growth trend in the same stage. The incubation period was dominated by creation of cavities, along with growth of a small amount of cavities. Area fraction of cavities was an appropriate parameter to describe surface changes in the incubation period of ceramics.