Ceramic Injection Molding Cold Sintering (CS)
The basic process of ceramic injection molding CS technology is to add a small amount of aqueous solution to the ceramic powder to wet the particles, and the surface material of the powder is decomposed and partially dissolved in the solution, thereby generating a liquid phase between the particle-particle interface. Put the wetted powder into the mold, heat the mold, and apply a large pressure at the same time. After maintaining the pressure and keeping it for a period of time, a dense ceramic material can be prepared. During this process, the microstructure of the ceramic material evolves. as the picture shows.
Although there are many systematic influencing factors of CS process, the equipment used by this technology is relatively simple. , The ceramic CS equipment mainly includes an ordinary press, two heating plates installed on the top and bottom of the press, and an electronically controlled heating jacket can also be wrapped around the mold for heating the powder.
Oscillating Pressure Sintering for Ceramic Injection MoldingCIM (OPS)
Various existing pressure sintering technologies use static constant pressure. The introduction of static pressure during the sintering process helps to eliminate pores and improve the density of ceramics, but it is difficult to completely ionize and covalently bond special ceramics. The exclusion of pores inside the material still has certain limitations for the desired preparation of ultra-high strength, high toughness, high hardness and high reliability materials.
The main reasons for the limitations of HP static pressure sintering are reflected in the following 3 aspects:
① Before the start of sintering and in the early stage of sintering, the constant pressure cannot fully realize the particle rearrangement of the powder in the mold to obtain a high packing density;
② In the middle and later stages of sintering, the plastic flow and the elimination of agglomerates are still limited, and it is difficult to achieve complete uniform densification of the material;
③ In the later stage of sintering, it is difficult to completely eliminate residual pores with constant pressure.
To this end, the author’s research group proposed a new design idea of introducing dynamic oscillating pressure to replace the existing constant static pressure in the powder sintering process, and took the lead in developing an OPS technology and equipment in the world. Under the action of a relatively large constant pressure, an oscillating pressure with adjustable frequency and amplitude is superimposed to turn the “dead force” applied in traditional sintering into “vigor”. The schematic diagram of the oscillating pressure coupling device and principle is shown in the figure.
The new OPS technology has unique advantages for the preparation of materials with near theoretical density (greater than 99.9% of theoretical density), low defects, and ultra-fine grain microstructure. and reliability offers a new approach.
Post time: Jun-10-2022