Why do we study PVD coatings in depth? Here is the answer.
Friction is the phenomenon of mutual obstruction between the surfaces of relatively moving objects. Friction can be divided into the following types:
◆ Internal friction: The phenomenon that hinders the relative movement between molecules that occurs inside a substance.
◆ External friction: The phenomenon of mutual obstruction between the surfaces of relatively moving objects.
◆ Static friction: Friction only when there is the relative movement trend.
◆ Dynamic friction: Friction in the relative movement.
◆ Sliding friction: The form of movement between the surfaces of object is the relative sliding.
◆ Rolling friction: The form of movement between the surfaces of objects is the relative rolling.
Wear refers to the loss or transfer of materials on the surface of the material due to friction. The study of wear was started late, after proposing the adhesion theory in the 1950s, the research of wear was carried out quickly based on subsequent development of a variety of surface analysis equipment in 1960s. Wear would affect the efficiency of the machine, reduce the reliability of the work, and even prompt the machine to be scrapped in advance.
The mechanical wear can be roughly divided into three stages:
The run-in stage - the new part is generally in this stage when it is firstly used, also the wear rate is high.
The steady wear stage - normal working phase of the part, and the wear rate is stable and low.
The acutely wear phase - the parts are about to be scrapped as the wear rate increases sharply.
The three stages of wear are as follows:
According to the classification of the wear mechanism, it can be summarized as follows:
◆ Abrasive wear, abbreviated as wear, is the wear caused by free hard particles or hard contours from outside on the friction surface.
◆ Fatigue wear, also called pitting. It is the wear caused by the material fatigue caused by the repeated deformation of the micro-volume of the friction surface material under the action of alternating friction.
◆ Adhesive wear, also called gluing. After the contour peak of the friction surface “cold welding” at each point of the interaction due to the instantaneous temperature rise and pressure, the material moves from one surface to the other during relative motion, and adhesive wear is formed.
◆ Erosive wear. It is caused by the hard substance or particles material that entrained in the fluid on the friction surface under the fluid impact.
The friction of mechanical components is universal and unavoidable. Friction leads to heating, temperature rising and energy loss or transfer, that is wear. Wear causes damage to the surface shape and dimensions of the part, which reduces the efficiency and reliability of the machine till it loses original working performance and causes sudden damage to the part. Currently, about 1/3 to 1/2 of the energy in the world's industrial sector is ultimately consumed by frictional mechanical parts in various ways. About 80% of the damage is caused by various forms of wear. If we can do our best to reduce the useless friction consumption, we can save a lot of energy. In addition, most of the fragile parts of mechanical products are scrapped and replaced due to wear that exceeding the limit. If the wear can be controlled and reduced, both maintenance and the cost of the equipment can be reduced, and the cost of manufacturing the parts and their required materials can be saved. So, reducing the friction and wear of mechanical components is critical to the development of the industry and the protection of the environment.