Experimental Characterization of Laser Trepanned Microholes in Superalloy GH4220 with Water-Based Assistance

An experiment using water-assisted millisecond laser trepanning on superalloy GH4220 was carried out, and the effects of pulse energy on the hole entrance morphology, diameter, roundness, cross-section morphology, taper angle, sidewall roughness, and recast layer in air and with water-based assistance were compared and analyzed. The results show that, compared with the air condition, the water-based assistance improved the material removal rate and hole quality, increased the diameter of the hole entrance and exit, increased the hole roundness, decreased the hole taper angle, decreased the hole sidewall roughness, and reduced the recast layer thickness. In addition, under the combined action of water and steam inside the hole, the sidewall surface morphology quality was improved. Compared with the air condition, the spatter around the hole entrance was reduced, but the oxidation phenomenon formed by the thermal effect surrounding the hole entrance with water-based assistance was more obvious. The research provided technical support for the industrial application of millisecond laser drilling

Microstructure and properties of ZrO2/Ni3Al-Ni3Al double-layer coating on stainless steel prepared by powder sintering one-step forming process

ZrO _2 /Ni _3 Al-Ni _3 Al double-layer coating on stainless steel was prepared by powder sintering one-step forming process. The surface-interface morphologies, chemical element distribution and phase compositions of the coatings before and after thermal oxidation or hot corrosion were analyzed using scanning electron microscope (SEM), energy dispersive spectrometer (EDS) and X-ray diffractometer (XRD). The microstructure of the coating was Ni _3 Al matrix with dispersed ZrO _2 particles, which was pure and compacted. The Ni _3 Al intermediate layer compactly formed between stainless steel substrate and ZrO _2 /Ni _3 Al composite coating, with good metallurgical bonding interfaces. The ZrO _2 /Ni _3 Al-Ni _3 Al double-layer coating exhibited a relatively high outmost microhardness of about 500 HV, and then gradually decreased from the coating to the substrate. When thermal oxidized or hot corroded at 1050 °C, a mixed oxide layer of NiO, Al _2 O _3 and NiAl _2 O _4 formed on the coating surface, which effectively acted as a diffusion barrier for oxygen and corrosive substances, and thus demonstrated the good protective effect of ZrO _2 /Ni _3 Al coating

Influence of ultrasonic vibration on percussion drilling performance for millisecond pulsed Nd:YAG laser

The ultrasonic vibration-assisted laser drilling is a recently emerging/growing new technique, especially in laser drilling. Differently from the previous work reported, this paper proposed to use the ultrasonic vibration (25 kHz) for assisting the millisecond pulsed Nd:YAG laser percussion drilling process to improve the drilling performance. Through comparing the drilled microholes without/using ultrasonic assistance, the influence of ultrasonic vibration on the drilled blind hole morphology/geometry, the hole wall surface roughness, the recast layer microstructure, and the hardness distribution of the heat affected zone for the drilled microhole was analyzed by altering laser pulse energy and/or laser pulse number. It was shown that the ultrasonic vibration incorporated into the laser drilling process might enhance the drilling efficiency in terms of the increase of hole depth and width. However, the drilled hole taper might be decreased via using ultrasonic assistance. Moreover, the ultrasonic vibration might clean the inner hole wall surface, and the microhole morphology/geometry could be improved through using ultrasonic assistance, resulting in a relatively clean and better-profiled hole wall with less defects and smaller taper due to the contribution of ultrasonic assistance. In addition, it was indicated that ultrasonic vibration might also improve the microhole heat affected zone hardness and reduce the inner hole wall surface roughness