Experimental Investigation of Vibration Damping Behavior of Magneto-Mechanical Coated AISI321 Stainless-Steel
Authors: Ashraf Hafiz Muhammad , Ali Farhan 
Published: January 2020

Abstract
High speed rotating machineries usually operate under severe conditions and enormous loadings and thus, are susceptible to several problems. One such problem that has caught the attention in recent decades is known as High Cycle Fatigue. More than 60 percent of rotating machinery failures has been attributed to this High cycle Fatigue. Along with High Cycle Fatigue, Vibration, an inherent phenomenon in machineries, also share its part in failure of rotating machineries. Rotating machinery components suffer from high amplitude vibrations when they pass through resonance. Stresses are developed as a result of these vibrations and fatigue in mechanical structures, providing a conducive environment for the development of cracks at Surface. When these surface cracks reach critical size, crack nucleation starts, which ultimately leads to catastrophic failures. So, in order to avoid the disastrous consequences, damping is needed. Damping keeps material’s integrity in case of impact forces, stresses due to thermal shocks in turbo machinery and earth quakes in huge structures. Thin layer of magneto elastic coating can be applied on substrate surface that acts as first line of defense. Large number of coating Processes are available around the globe. The optimized combination of coating material, substrate material and coating technique according to specific application is necessary. These coatings have the capability to combat the phenomenon of oxidation, wear and fatigue acting as a barrier between substrate and hostile environments. Further, they enhance the damping characteristics, and thus allows the high-speed rotating machinery to reach its operational speed without any failure at resonance. In this way, they not only enhance the performance of components in aggressive environments, but also improve the life cycle, saving assets of millions of dollars’ worth. This research is an endeavor to experimentally investigate effect of magneto mechanical coating on damping of AISI 321 Stainless steel. AISI 321 was selected as base material because of its wide applications in engine components of gas turbines, heat exchangers and in different chemical industries. Two types of Air plasma sprayed magneto-mechanical powder (NiAl & CoNiCrAlY) were coated on base material and thickness was maintained up to 250μm in both the cases. Experiments were designed and performed on cantilever beam specimens for dynamic response measurement. Dynamic response of the system was measured to investigate the modal parameters of natural frequencies, damping ratio and time of vibration decay. For damping ratio, vibration analyzer mode was adjusted in time domain and beam was excited by using a hammer. Vibration analyzer showed the vibration decay as a function of time. Logarithmic decrement method was used to calculate the damping ratio in both cases. Dynamic response of all the three cases (NiAl coating, CoNiCrAlY and uncoated AISI321) were compared. Results were very reassuring and showed a significant improvement in damping characteristics.