Influence of Magnetron Sputtering Parameters on Speckle Characteristics for Application in Microscale DIC of Maraging Steel

Magnetron sputtering was utilised to deposit submicron-sized speckle patterns for microscale digital image correlation (DIC) of 18Ni-300 maraging steel. A Taguchi orthogonal array consisting of four configurations was used to investigate the influence of magnetron sputtering parameters (i.e. sputter current, sputter duration, and chamber pressure during sputtering) on the resultant speckle characteristics. Increasing the sputter current resulted in larger-sized speckles, while increasing the sputter duration resulted in larger-sized speckles at expenses size uniformity of speckles. A higher chamber pressure retards the transport of speckles resulting either in low deposition rate or much less uniform sizes of speckles. Among the configurations studied, configuration I (75 mA, 240 s, 3 Pa) produced speckle patterns that were most suitable for microscale DIC as its speckles were adequately smaller and more uniform in size. In-situ tensile test with DIC strain distribution mapping on sample deposited with speckle pattern configuration I shows a strain resolution of about 71 nm, and slip bands with widths measured between 240 to 400 nm, indicating the speckle pattern was suitable, enabling further study on deformation mechanism.