Carbide is one of the widely used metals in the manufacturing industry because of its incredible properties. Some of the excellent properties of carbide include high hardness, strength, and high wear resistance. It is among the metals that can withstand high abrasive conditions. That’s the reason it is widely used as the main materials for tools such as drilling bits, milling cutters, car cutters, planers, mulching teeth, boring knives, and so on.
To improve its mechanical properties, carbide is alloyed with other components to make it harder and stronger. Cobalt is one of the components added to the green material (or un-sintered carbide) to make it better for industrial use. Sintering is the process through which carbide is fused with cobalt at high temperatures. There are several variations of carbide sintering, including hydrogen, sinter-HIP, and vacuum sintering. Carbide vacuum sintering is the most widely used process.
The carbide vacuum sintering is a sintering process that is done below atmospheric pressure. It is both a chemical and physical process, which includes a number of processes like plasticizer removal, degassing, alloying, dissolving, and many others. In this guide, we look at four of major processes of carbide vacuum sintering
#1: Plasticizer Removal Stage
The plasticizer removal stage is where the material that increases the plasticity of the carbide is removed. The aim is to allow for easy alloying with another material to form a stronger carbide. The process starts at room temperature at about 200 ℃ when the carbide material or blank is heated in a vacuum. The temperature varies depending on the kind of plasticizer, and sometimes, it could reach up to 500℃.
The metal powder particles start absorbing the gas under the effect of heat, a process also referred to as the gasification temperature. As the carbide material surface absorbs heat, the plasticizer is dislodged and starts to thermally escape off the pressured bank. The high vacuum levels facilitate the lifting and the escaping of the gas. That’s how the removal of the plasticizer is carried out during carbide vacuum sintering.
2#: Pre-Burning Phase
The pre-burning phase is the second stage in the carbide vacuum sintering process. The process is crucial as it helps to get rid of the oxygen and carbon reaction, affecting the preceding processes. Note that the reaction of oxygen and carbon gases can lead to the generation of carbon monoxide gas. If this gas is not removed or avoided from forming, then it could cause closed pores in the carbide-cobalt alloy during the pressurized sintering.
On the other hand, if oxygen is not removed, it could cause oxidation. This may cause serious effects on the wetness of the material during the hardening phase of the carbide. That’s the reason why degassing these gases is very crucial when during the vacuum sintering process.
#3: High-Temperature Sintering Stage
The high-temperature sintering stage is when the alloying or combination of the carbide and cobalt materials occurs. The process takes place under very temperature, and there are key parameters that must be maintained for the desired results to be achieved. One of them is the sintering temperature. Depending on the grades of the materials used, the temperature may vary. You need to get the right sintering temperature.
The other essential parameter is the sintering time. This is one thing that you must get right because heating less or more will affect the quality of the product. However, the two elements depend on the kind of alloy compositions. Factors such as powder granularity, grinding strength, and so on are very crucial. The design of the material could also be an essential factor.
#4: The Cooling Phase
The cooling phase, also known as the heat treatment phase, is helpful in improving the hardness and strength of the formed carbide material. The cooling speed is the most crucial factor to consider because it determines the bonding process of the composition.
Cooling speed also determines the structural features, such as the creation of internal stress. The control of the cooling speed is crucial for this final phase of the vacuum sintered carbide. Make sure that you have gotten it right temperature to ensure the desired quality is achieved.