Surface integrity analysis of ADI and IADI after manufacturing processes

A.D. SOSA; M.E. FURNO; D.A. COLOMBO

Darmstadt

Congreso; Materials Science and Engineering 2018 (MSE); 2018

Darmstadt University of Technology

Ductile iron (DI) is a candidate material for the manufacturing of mechanical parts when low costs, recyclability and reliability are needed.It also offers an excellent weight to strength ratio, comparable with more expensive light alloys. Mechanical properties of DI can be widely changed by heat treatment, to get other variants like austempered ductile iron (ADI) and intercritical austempered ductile iron (IADI).ADI parts are common in supports, pumps and engines exposed to marine conditions. IADI is a most recent development for mechanicals components that need more toughness than ADI parts. When considering thin wall parts, the higher surface-to-volume ratio makes surface properties essential for quality and service performance.The operations required for the manufacturing of mechanical parts, such as turning, grinding and coatings deposition, among others, modify the properties and characteristics of their surfaces. The proper use of process parameters and the knowledge of their effect on surface properties can lead to optimize the service behavior of them.This work studies the surface characteristics (hardness, topography, residual stresses, microstructure) of DI samples subjected to different manufacturing processes (heat treatment, turning, grinding and coatings deposition) and its correlation with shape distortion and other properties such as corrosion and wear resistance.Surface integrity of samples was determinated by means of microindentation tests, surface scanning, X-ray diffraction optical and scanning electron microscopy. Furthermore, corrosion and wear behaviour of surfaces were analized by means of electrochemical experiments on sea water and unidirectional sliding - rolling contact fatigue tests. The analysis was carried out by comparing the properties of the material before and after the manufacturing process applied.The results indicate that machining (both conventional and abrasive) and coatings deposition produces surface hardening, compressive residual stresses in most cases and topographic changes at macro and micro-scale. In addition, machining generates plastic deformation in surface and sub-surface layers and shape distortion in thin wall samples, diminishes the corrosion resistance and does not affect significantly the wear resistance while coatings deposition improves in most cases the corrosion and wear behaviour.