Papers by Keyword: Nanoindentation Hardness

Abstract: The paper focuses on the surface damage of quartz glass in multiple grinding, so as to find out the machining parameters that can improve the surface quality of quartz glass. Molecular dynamics (MD) method is adopted to machine the quartz glass. Firstly, the initial grinding is done on quartz glass with the depth of 12 Å. Based on the initial grinding, no feed grinding processes are done for three times separately and the feed grinding processes are carried out on the damage layer left by the previous process. By the coordination number (CN), machined surface topographies of quartz glass are gained and regions of densification are marked. Moreover, the damage layer thickness of different machined surface is also calculated. By analyzing the density of different surface damage layers, the regulation of the density distribution is obtained. Finally, the nanoindentation hardness is gained by different load-displacement curves in nanoindentation simulation. The results show that the first no feed grinding and the second feed grinding can improve the accuracy and quality of grinding. Too many no feed grinding processes and other feed grinding processes will induce serious damage of the machined surface, which is clearly showed in the obvious increase in the density, hardness and thickness of the damage layer. At last, the results of the density analysis and nanoindentation also proved that the densification and hardness of quartz glass cannot increase unlimited. The results can be applied in the ultra-precision grinding of quartz glass to control the thickness of damage layer and improve the quality of processing.

Abstract: Effect of annealing temperature on microstructures and properties of warmly deformed SCRAM (Super-clean Reduced Activation Martensitic) steel on Gleeble-3500 thermo-simulation machine was investigated. The results showed that an increase in the annealing temperature can result in increasing the martensitic lath width from 0.48 um to 0.65 um and decreasing the dislocation density from 6.4×10¹⁵ m^-2 to 2.8×10¹⁵ m^-2 in SCRAM steel. The specimen exhibited high reduction of area and total elongations when the annealing temperature is up to 600 oC. The tensile fracture surface observation indicated that dimples became more uniform and deeper and cleavage fracture traces disappeared with the annealing temperature increasing. The irradiation-induced helium bubbles and hardening were observed in all the specimens after helium implantation to 1e + 17/cm² at 450 oC. The helium bubbles became larger but less when the annealing temperature increased. The optimal annealing temperature is 450 oC in this experiment.

Abstract: A novel polishing technique combined with the irradiation of atmospheric pressure plasma known as plasma assisted polishing (PAP) is proposed for the finishing of difficult-to-machine materials. In this paper, we mainly focus on the case of 4H-SiC substrate. We used helium-based water vapour plasma to modify the mechanical and chemical properties of the SiC surface. The results of X-ray photoelectron spectroscopy (XPS) measurements indicate that the surface was efficiently oxidized after plasma irradiation, and the main product was silicon oxide. A small amount of silicon oxycarbide was also observed which was identified as the interface oxide. The result of a nanoindentation test revealed that the hardness of oxidized SiC surface decreased by one order of magnitude compared with the unprocessed surface. The decrease of hardness of modified surface enables us to flatten the surface without forming any scratches and subsurface damage by using soft abrasive compared with the base material. We used CeO₂ as the abrasive material in PAP, the hardness of which was near to that of the oxidized surface. The microscopic interferometer images of the PAP processed surface showed us that scratches disappeared and surface roughnesses also decreased from 4.410 nm p-v, 0.621 nm rms to 1.889 nm p-v, 0.280 nm rms. From the atomic force microscopy (AFM) images, a step and terrace structure was observed on the surface after PAP, which means that an atomically flat surface was obtained. We conducted reflection high-energy electron diffraction (RHEED) measurement to evaluate the residual strain of the PAP processed surface. The results indicate that the lattice constants approached the ideal value, which meansthat the PAP technique did not introduce crystallographical subsurface damage.

Abstract: Tantalum (Ta) thin film was deposited onto Si (100) substrates using direct-current magnetron sputtering. The structure and mechanical properties of Ta films were investigated by X-ray diffraction, Field emission scanning electron microscope, and nanoindenter. The results indicated a transition from regular to irregular Hall-Petch relationship with decreasing grain size. Besides, a peak indentation hardness value of 12.8 GPa, much higher than that of bulk coarse-grained Ta, was obtained at the grain size of 36.3 nm.

Abstract: Conventional coating tools have a high affinity for ductile materials, like aluminum alloy, so cutting chips tend to adhere to cutting edge and work material surface. Therefore, chipping is caused, and surface texture is degraded. In order to solve these problems, recently, DLC (Diamond-Like-Carbon) has been applied to coating material. In this research, it is curried out cutting of Aluminum alloy by the use of DLC coating tool, and examined influence of DLC coating conditions on cutting characteristics. So far we have been concerned with the effect of type of hydrocarbon gas (acethylene:C2H2, methane:CH4) on cutting. As a result, it is revealed that cohesion of chips decreases, and surface roughness of work material improves in the case of acethylene-DLC. On the other hand, internal stress is produced by deference in hardness between tool surface and DLC film, and which is considered cause of film peeling [1]. Therefore, we examined interlayer between DLC film and tool surface in order to relax of internal stress. As a result, it was cleared that Titanium interlayer excels in adhesion.

Abstract: Sliding wear and hardness tests in Ni/Cu multilayers electrodeposited on polycrystalline copper substrate were carried out. The multilayers had a total thickness of 5 μm and an individual layer thickness from 5 to 100 nm. Hardness of the multilayers measured with a nanoindentation tester was found to be dependent on layer thickness. The multilayer with the layer thickness of 20 nm showed the highest value among them. It was found that the wear resistances of all the multilayers tested were higher than that of an electrodeposited nickel coating. It was also revealed that the specific wear rate of multilayers decreased with decreasing the layer thickness although the highest hardness was attained at the 20 nm layer thickness. Scanning ion microscope observation showed that the subsurface area kept the layered structure of nickel and copper even after sliding wear. The multilayer had plasticity sufficient to accommodate deformation coming from the sliding wear, because fine grains peculiar to severe plastic deformation process were formed near the worm surface.

Abstract: In material nanoindentation hardness testing, the hardness will decrease with the indentation depth or peak load increase, i.e. indentation size effect (ISE). There are several models and equations were proposed to describe ISE. But the variables self-inaccurate in these models and equations, it will affect the result trueness. Single crystal silicon was used for nanoindentation experiments, and max depths were obtained from these experiments. Combining Matlab software, residual areas were obtained by atomic force microscopy (AFM). Based on max depth and residual area, a new model—residual area max depth model was proposed for indentation size effect in nanoindentaion hardness. The new model perhaps can understand and describe ISE in indentation hardness better than other models and equations.