Necessity to Make Silicon Nitride Ceramic Micro Components
High strength, high temperature resistance, superior oxidation resistance, and low weight are all benefits of silicon nitride ceramics. Their use in micro-electromechanical systems (MEMS) technology has drawn attention recently. The silicon wafer micro-fabrication technique is currently in a fairly advanced stage. Single-crystal silicon wafers may be transformed into two-dimensional or three-dimensional microstructures with complex shapes using mask and photolithography techniques. However, due to the quick advancement of MEMS technology, monocrystalline silicon is unable to satisfy some unique needs. For instance, high-temperature and oxidation-resistant materials must be utilized in high-temperature applications for nano-turbines, micro-burners or reactors, high-temperature pressure sensors, etc.
Silicon nitride ceramics are suited for usage as high-temperature components of power MEMS due to their high melting point, high strength and hardness, oxidation resistance, chemical corrosion resistance, and lower specific gravity. However, silicon nitride is tough and non-conductive; even standard cutting is challenging. Additionally, little study has been done on micro-molding procedures that use silicon nitride powder as a starting material because of the high sintering temperature needed for silicon nitride (>1800°C).
As a result, the goal of this article is to present a method for manufacturing silicon nitride ceramic micro-components, i.e., a method that combines reaction sintering with micromachining of a porous silicon pre-sintered body to produce a silicon nitride ceramic micro-component with a comparatively simple process. It is appropriate for creating delicately shaped silicon nitride ceramic fine components because it combines the machinability of the pre-sintered body made of silicon powder with the near-net-size forming properties of the silicon nitride reaction sintering.
Manufacturing Steps of Silicon Nitride Ceramic Micro Components
The approach is to treat porous silicon into micro-structures before nitriding to generate silicon nitride ceramic micro-components with unchanged accuracy and size. Here are the specific steps:
Preparation of Powder Raw Materials
Si powder is utilized as the raw material, pure ethanol is used as the grinding medium, and wet ball milling is used to crush the Si powder. The ball milling process refines the Si powder to a diameter of 3-6 um by using silicon nitride balls and a tank lined with silicon nitride.
Pre-Sintered
Utilizing a hot pressing equipment or a plasma discharge sintering machine, the silicon powder is placed into a graphite mold and pre-sintered. In this procedure, the sintering temperature is kept between 1000 and 1300°C, resulting in a relative density of 70 to 85% for the silicon powder that was placed in the graphite mold before sintering. The pre-sintering temperature is maintained for 3 minutes before the temperature is decreased. The heating rate for the aforementioned plasma discharge sintering is 100° C./min.
Processing Silicon Powder Pre-Sintered Body into Flakes
After the silicon powder calcined body has been removed from the graphite mold, the body is next carved into thin slices. This process is repeated several times. The machined sheet has a thickness of 1-5 millimeters and a diameter ranging from 5-40 millimeters.
Micro Machining of Flakes
Using a micro EDM machine or a precision grinding machine, the flakes are micro machined.
Nitriding Treatment
Nitriding is accomplished by placing the finished product on top of boron nitride particles that have been spread out on the bottom of a graphite or silicon nitride crucible and then placing the crucible in an electric furnace chamber filled with nitrogen. The nitriding treatment is performed at temperatures ranging from 1300 to 1450°C.
Advantages and Effects of the Method
This method enables the micromachining and micromolding of silicon nitride ceramic microcomponents by fusing the properties of silicon nitride ceramic reactive sintering and micromachining. The silicon powder has a certain density and enough strength after pre-sintering. However, as compared to silicon nitride ceramics, it has a relatively low hardness and may be machined swiftly using cemented carbide tools. Additionally, the pre-sintered body made of silicon powder can be treated using methods other than electric ignition, including photolithography and reactive ion etching. Only through nitriding in nitrogen is it possible to generate silicon nitride ceramic components with high temperature resistance, corrosion resistance, and wear resistance following microstructure processing.