In situ microscopic study of tribology and growth of ZDDP antiwear tribofilms on an Al-Si alloy

Zincdialkyldithiophosphates (ZDDPs) form protective antiwear tribofilms but the growth mechanism and their contribution to friction on non-ferrous alloys are not well understood. Using a recently developed in situ AFM technique, we monitor the growth of ZDDP based tribofilms, friction, and wear, over Al matrix and Si phase of ADC12, sliding against a nonferrous alumina probe. Sliding tests performed at elevated temperature (110 degrees C), simultaneously over Al and Si phase, reveal tribofilm growth on both Al and Si regions without noticeable wear. However, the tribofilm thickness, density, and coefficient of friction on the Si phase are higher than on the Al matrix. Significant wear and increase in the coefficient of friction was observed when sliding within the Al matrix region alone.