Effect of Thermal Softening on Anisotropy and Ductile Mode Cutting of Sapphire Using Micro-Laser Assisted Machining

Abstract

Ceramics and semiconductors have many applications in optics, micro-electro-mechanical systems, and electronic industries due to their desirable properties. In most of these applications, these materials should have a smooth surface without any surface and subsurface damages. Avoiding these damages yet achieving high material removal rate in the machining of them is very challenging as they are extremely hard and brittle. Materials such as single crystal silicon and sapphire have a crystal orientation or anisotropy effect. Because of this characteristic, their mechanical properties vary significantly by orientation that makes their machining even more difficult. In previous works, it has been shown that it is possible to machine brittle materials in ductile mode. In the present study, scratch tests were accomplished on the monocrystal sapphire in four different perpendicular directions. A laser is transmitted to a diamond cutting tool to heat and soften the material to either enhance the ductility, resulting in a deeper cut, or reducing brittleness leading to decreased fracture damage. Results such as depth of cut and also nature of cut (ductile or brittle) for different directions, laser powers, and cutting loads are compared. Also, influence of thermal softening on ductile response and its correlation to the anisotropy properties of sapphire is investigated. The effect of thermal softening on cuts is studied by analyzing the image of cuts and verifying the depth of cuts which were made by using varying thrust load and laser power. Macroscopic plastic deformation (chips and surface) occurring under high contract pressures and high temperatures is presented.

Recent Advances in Micro/Nano-cutting: Effect of Tool Edge and Material Properties

“…In laser beamassisted cutting of silicon, the surface roughness was improved and the radial spokes which are caused by the crystallographic orientation effect can be eliminated [209]. The anisotropy effect of the single-crystal C-plane sapphire on the ductile mode cutting was investigated in laser-assisted cutting technology [210]. The results showed that for different cutting directions, the critical UCT was improved by applying this technology.…”

“…It is widely used in processing of materials [218], such as cutting, welding, marking and sintering. Besides that, it is also used in assisting the cutting of brittle materials, such as the silicon [209] and sapphire [210]. In laser beamassisted cutting of silicon, the surface roughness was improved and the radial spokes which are caused by the crystallographic orientation effect can be eliminated [209].…”

“…Therefore, the machining efficiency is relatively low and the machined surface quality could not attain a stable status due to the other factors in cutting process. To improve the machinability of brittle materials, many assistant methods, such as the ultrasonic elliptical vibration assistant [207], laser beam assistant [208][209][210] and surface modification methods [211][212][213], have been proposed. Ultrasonic vibration-assisted cutting which is an effective method in diamond cutting of ferrous metals [214][215][216] was also a method in improving the machinability of brittle materials [207].…”

A Review on Micro- and Nanoscratching/Tribology at High Temperatures: Instrumentation and Experimentation

“…In other words, at high temperatures, plasticity plays a greater role in the fracture and deformation processes primarily as a result of thermally generated defects and thermal softening processes (Ref 83,84). Accordingly, to further augment the ductile response of hard-brittle materials, the machining process can be coupled with a heat source, e.g., laser (Ref [85][86][87][88][89]. Recently, SPDT has been coupled with the l-LAM technique to preferentially heat and soften the high-pressure metallic phase during scratching/cutting.…”

Laser-Induced-Plasma-Assisted Ablation and Metallization on C-Plane Single Crystal Sapphire (c-Al2O3)

“…In fact, the preferable absorption wavelength of sapphire is about 200 nm [ 11 , 12 , 13 ]. There are several methods of processing SCS, such as ultrasonic assisted grinding process [ 14 ], UV laser cutting, micro-laser assisted machining [ 15 , 16 ], and LIPAA.…”