Zhang Y, Guo T, Li Z, Li C
Fourth Military Medical University.
Hua Xi Kou Qiang Yi Xue Za Zhi. 2000 Oct;18(5):294-7.
To investigate the influence of the mold temperature on the surface reacted layer of Ti-Zr alloy castings.
Ti-Zr alloy was casted into a mold which was made of a zircon (ZrO2.SiO2) for inner coating and a phosphate-bonded material for outer investing with a casting machine (China) designed as vacuum, pressure and centrifuge. At three mold temperatures (room temperature, 300 degrees C, 600 degrees C) the Ti-Zr alloy was casted separately. The surface roughness of the castings was calculated by instrument of smooth finish (China). From the surface to the inner part the Knoop hardness and thickness in reacted layer of Ti-Zr alloy casting was measured. The structure of the surface reacted layer was analysed by SEM. Elemental analyses of the interfacial zone of the casting was made by element line scanning observation.
The surface roughness of the castings was increased significantly with the mold temperature increasing. At a higher mold temperature the Knoop hardness of the reactive layer was increased. At the three mold temperature the outmost surface was very hard, and microhardness data decreased rapidly where they reached constant values. The thickness was about 85 microns for castings at room temperature and 300 degrees C, 105 microns for castings at 600 degrees C. From the SEM micrograph of the Ti-Zr alloy casting, the surface reacted layer could be divided into three different layers. The first layer was called non-structure layer, which thickness was about 10 microns for room temperature group, 20 microns for 300 degrees C and 25 microns for 600 degrees C. The second layer was characterized by coarse-grained acicular crystal, which thickness was about 50 microns for three mold temperatures. The third layer was Ti-Zr alloy. The element line scanning showed non-structure layer with higher level of element of O, Al, Si and Zr, The higher the mold temperature during casting, the deeper the Si permeating and in the second layer the element Si could also be found.
The mold temperature is one of the major factors influencing to casting quality. In order to reduce the surface reacted layer of Ti-Zr alloy castings, the lower mold temperature and the investment without Si should be chosen.
研究铸型温度对Ti-Zr合金铸件表面反应层的影响。
采用国产真空、压力和离心铸造机，将Ti-Zr合金浇铸到由锆英石（ZrO₂·SiO₂）作内涂层、磷酸盐粘结材料作外铸型的铸型中。在三个铸型温度（室温、300℃、600℃）下分别浇铸Ti-Zr合金。用国产光洁度仪计算铸件的表面粗糙度。测量Ti-Zr合金铸件从表面到内部反应层的努氏硬度和厚度。用扫描电子显微镜分析表面反应层的结构。通过元素线扫描观察对铸件界面区进行元素分析。
铸件的表面粗糙度随铸型温度升高而显著增加。铸型温度较高时，反应层的努氏硬度增加。在三个铸型温度下，最外层非常硬，显微硬度数据在达到恒定值时迅速下降。室温及300℃铸件的厚度约为85微米，600℃铸件的厚度为105微米。从Ti-Zr合金铸件的扫描电子显微镜照片看，表面反应层可分为三个不同的层。第一层称为非结构层，室温组厚度约为10微米，300℃时为20微米，600℃时为25微米。第二层的特征是粗晶针状晶体，三个铸型温度下其厚度约为50微米。第三层是Ti-Zr合金。元素线扫描显示非结构层中O、Al、Si和Zr元素含量较高，铸造时铸型温度越高，Si渗透越深，在第二层中也能发现Si元素。
铸型温度是影响铸件质量的主要因素之一。为减少Ti-Zr合金铸件的表面反应层，应选择较低的铸型温度和不含Si的铸型材料。
