Consolidation of low-sinterability powders with applying medium isostatic pressure

在可控气氛和压力为室温至10kg/cm^2的烧结炉上，对各种合金和陶瓷粉末进行了烧结实验。粉末特性、烧结温度、施加压力、烧结时间、加热和冷却条件对烧结坯的相对密度和晶粒尺寸的影响。铁合金和超级合金粉末在10kg/cm^2的压力下可以致密到全密度。金属/硼化物体系的工具合金粉末在如此低的压力下无法充分致密化，需要达到500kg/cm^2的高压才能充分致密化。利用图像分析仪对晶粒组织、残余孔隙分布、析出相形状和尺寸进行了定量分析，研究了微观组织演变过程中的烧结机理。采用非接触式膨胀分析仪测量了烧结收缩率，并借助计算机模拟烧结致密化动力学，推导了收缩率的动力学方程。目前，仿真结果与实验结果的一致性并不好。然而，对致密化驱动力的性质进行了澄清，并对施加压力对致密化增强的影响进行了半定量的讨论。为了进一步了解烧结机理，建立了考虑烧结温度、压力、时间和气氛影响的烧结图。利用这张烧结图，讨论了加压对烧结机理的影响。

Sintering experiments were conducted on various alloys and ceramics powders using a sintering furnace with controllable atmosphere and pressure of ambient to 10kg/cm^2. The effects of powder characteristics, sintering temperature, applied pressure, sintering time, and heating and cooling conditions on the relative density and grain size of the sintered compacts. Iron alloy and super alloy powder could be densified to full density with pressure of 10kg/cm^2. Tool alloy powder of metal/boride system could not be sufficiently densified with such low pressure, and the higher pressure up to 500kg/cm^2 was necessary for the full densification. The grain structures, distributions of residual pores, shape and size of the precipitate were quantifield with an image analyzer, the sintering mechanisms during the microstructural evolution was studied. The sintering shrinkage rate was measured by non-contact-type dilatometric analyzer, and with the aid of the computer simulation of sintering densification kinetic equations for the shrikage rate were derived. At present the agreement between the simulation and the experimental is not good. However, the nature of the driving force for the densification was clarified, and the semi-quantitative discussion can well be made about the effect of applied pressure on the densification enhancement. For the further understanding of the sintering mechanisms a sintering map which takes into account the effects of sintering temperature, pressure, time and atmosphere has been constructed. With this sintering map the effect of pressurizing has been discussed in correlation with sintering mechanisms.