The test materials were high hardness T130A cermet and SKD11 tool steel. The microstructure and chemical composition of SKD 11 steel is shown in Figure 2 and Table 1 . The workpiece was machined by a wire electro-discharge machining (Wire EDM). The dimension of the specimen was around 10 mm × 5 mm × 10 mm. The parameter of micro particle bombarding (MPB) included air pressure (lower condition A and higher condition B) and bombarding time, such as 15, 20, 25, and 30 sec, respectively. Figure 3 and Figure 4 show the particle data of micro particle bombarding (MPB).
The microstructure and composition of the material were observed with scanning electron microscope (SEM, HITACHI SU-5000, Japan and Zeiss AURIGA, Germany) and energy-dispersive X-ray spectroscopy (EDS). The surface was photographed and analysed at a working voltage of 20 KV and a magnification of 500×. The phase composition and residual stress were analyzed by a Bruker D8 X-ray diffractometer, the compound phase composition was analyzed by the working voltage of 50 KV, and the residual stress was analyzed by the sin2ϴ method. The roughness was measured using a 3D laser confocal microscope (Figure 5 , VK-X200 series, Keyence, Japan). The vickers hardness (HV) was used to identify the hardness after micro particle bombarding (MPB).
The microstructure and composition of the material were observed with scanning electron microscope (SEM, HITACHI SU-5000, Japan and Zeiss AURIGA, Germany) and energy-dispersive X-ray spectroscopy (EDS). The surface was photographed and analysed at a working voltage of 20 KV and a magnification of 500×. The phase composition and residual stress were analyzed by a Bruker D8 X-ray diffractometer, the compound phase composition was analyzed by the working voltage of 50 KV, and the residual stress was analyzed by the sin2ϴ method. The roughness was measured using a 3D laser confocal microscope (