Solving wear and erosion (tribology) problems
While there are many strategies for solving wear and erosion (tribology) problems, the solution process begins with first establishing the mechanism and the causes for the specific part. it is necessary to understand the mechanical loading/operating conditions, the presence or lack of a lubricant and its mode of operation, i.e., hydrodynamic or boudry lubricant, and the material behavior. The material behavior in the wear couple identifies the type of wear, i.e., adhesive (galling), abrasive, erosive, etc. Once the type of wear is established, ether changes to the mechanical operating conditions/design, the lubricant, or the material/coatings can be employed to solve the problem.
We have extensive experience with physical vapor deposition (PVD) ceramic coatings such as titanium nitride (TiN) and titanium carbo-nitride (TiCN).. These are the often nano crystalline gold coatings commonly found on high performance parts and cheep drill bits. Just because it is gold colored does not mean it has good wear resistance. In many optimized applications, TiN and TiCN are multi-layered. These coatings require strict process control and post processing if they are to work.TiN, for example is a non stoichiometric compound, and the ratio of titanium to nitrogen is a critical performance parameter. Poor coatings are plagued with residual stress problems leading to adhesion issues and high wear rates to the counter face material. However, these are solvable problems. We can help you deal with these challenges.
Not all wear problems involve sliding of two materials. Erosion can be caused by particles entrained in a fluid impacting the surface. Erosion can also occur during cutting, slicing or slitting operations if hard contaminant particle are on the material to be cut. These erosive materials may also simply be part of the process stream, such as in agricultural processing, food processing, and wine making. We have experience, backed up by publications, that can help you.
Cavitation causes another type of erosive wear, displaying characteristic pock marks on the material surface. We have designed and built ASTM G32 cavitation test machines and performed research on mechanisms of cavitation in fluids and hydrocarbons.
Sometimes it is necessary to design a wear test machine or tribometer to screen materials. Our experience is that the best results obtain from a purpose built machine that simulates as closely and economically possible the real operating conditions. We have experience with the design of tribometers for sliding (reciprocating and continuous rotation) wear, and abrasive wear in dry, lubricated, and high temperature environments..
Examples of our tribological work
The micrographs below from our work on tribology illustrate various wear situations and what can be learned both about the material choice and mechanical loading simply from studying the part.
Electrical contact sliding wear and corrosion. The bright field image shows wear and corrosion, but does not really provide much information on the depth of wear resulting from repeated sliding insertion and removals. The dark field image combined with critical focusing on the Nomarski image establishes that the corrosion is in-fact on top of the contact substrate. The Nomarski contrast image then reveals the surface topography of the wear grooves, showing much more extensive damage than anticipated by the simple bright field image. Thus, corrosion appears to be a continuous process and sliding wear is an intermittent process.