Advanced Materials Research Vol. 797

Abstract: Double-substrate angle polishing is presented for detecting depth of sub-surface damage layer during sapphire substrate grind process. Bimorph overlap bond is used in the double-substrate angle polishing, and when measuring the beveled corrosion crack, measurement errors caused by the traditional angle polish which results in fussy boundaries between polished bevel and the edge of the original wafer plane is avoided. Also digital length measurement is used to measure specimens polished bevel machining contours, then calculate accurate slant angles, eliminate errors of inaccurate angle values and improve measurement accuracy. This experiment has tested the length of mono-crystal polished bevel crack is 175um, the angle of slant is 4.85°. According to theoretical calculation, the double-sided grinding substrate subsurface damage layer is 15um, and the depth of double-sided crystal surface is about 30um. Grinding parameters: 320# boron carbide aqueous solution, lapping pressure 110g/cm², grinding speed 30r/min.

Abstract: The presented approach evaluates the application of the surface integrity of machined components as load sensors. Residual stress relaxation due to mechanical load is utilized to retrieve information on the load history of a component. The critical load stress, the sensitivity and the relaxation gradient are quantified and analyzed for AISI 1060 steel. More specifically, the influence of heat treatment and therefore of the materials ultimate strength has been evaluated. The results show that the knowledge on the error determining the residual stress is crucial for the accuracy of the approach. Furthermore, a sufficient relaxation gradient has to be provided by low residual stress sensitivity and high initial residual stress magnitude. Both properties can be influenced by heat treatment and machining.

Abstract: Wire saw process is widely used in the machining of hard and brittle materials with low surface damage and high efficiency. Cutting of silicon wafers in integrated circuit (IC), semiconductor and photovoltaic solar industries is also generally using wire saw process. However, the surface layer damage induced by wire saw process will seriously decrease the wafer quality and increase the process time and production costs of the post grinding and polishing. The surface layer qualities of the silicon wafers sawed by the different wire saw processes was investigated in this paper. The characteristics of surface roughness, surface topography and subsurface damage of silicon wafers sliced by the fixed abrasive and the loose abrasive wire sawing respectively were compared and the corresponding reasons were analyzed.

Abstract: The machining methods such as waterjet cutting, milling, grinding, lapping, etc. are usually used to manufacture glass fiber reinforced composites (GFRCs) parts. Damages will be produced unavoidably in the machining process, no matter which machining method is employed. Subsurface damage is one of the important parameters to evaluate the surface layer damages. The detection method for the subsurface damages of glass fiber reinforced glass matrix (glass/glass) composite after machining is researched. The characteristics of subsurface damages of glass/glass composite after waterjet cutting, milling, grinding and lapping are investigated mainly, when the fiber direction is either perpendicular or parallel to the cutting surface.

Abstract: Hydroxyapatite (HA) coating of hard tissue implants is widely employed for its biocompatible and osteoconductive properties as well as its improved mechanical properties. In this study, a novel micro-blasting process has been used to successfully modify a titanium alloy substrate with a HA treatment using a dopant/abrasive regime. The impact of a series of apatite abrasives, was investigated to determine the effect of abrasive particle size on the surface properties of both micro-blasting (abrasive only) and continuous (HA/abrasive) treatments. The resultant HA treated substrates were compared to substrates treated with abrasive only (micro-blasted) and an untreated Ti. The HA powder, apatite abrasives and the treated substrates were characterized for chemical composition, coating coverage, crystalline and topography. The results show that the surface roughness of the HA blasted modification was affected by the particle size of the apatite abrasives used. This study demonstrates the ability of the continuous process to deposit HA coatings with a range of surface properties onto Ti alloy substrates. The ability of the continuous technology to offer diversity in modifying surface topography offers exciting new prospects in tailoring the properties of medical devices for applications ranging from dental to orthopedic settings.

Abstract: Strengthening of glass sheets through the process of ion exchange have been widely used in thinner cover glass for smart phone. The compressive stress improves the ability of the glass surface to withstand damage from mechanical impact. However, the presence of the damage resistant layer makes conventional mechanical and laser cutting of the ion-exchanged glass difficult. Normally, the cutting process will lead to spontaneous glass sheet breakage or shattering. Even successful in some samples, the underlying central tension is exposed on the edge, and the mechanical strength and durability of this edge is degraded. The repair of edge cracks becomes an extremely important issue for the development of single glass based smart phone. The ion exchanged glass plates (Corning IOX-FS) with a thickness of 0.7 mm were selected as the substrate materials. After cutting ion exchanged glass by high penetration diamond scribing wheels, the edge of glass plates can be protected or strengthened with silica sol using roll coating process. It was observed that the strength could be improved achieving 210 % compared to the strength of uncoated glass sheets. The sol-gel coating could improve the strength of the glass mainly by the mechanisms of filling in edge flaws or blunting crack tips. The effects of silica sol and processing parameters of roll coating process on the cracks filling effects were investigated.

Abstract: Tungsten based products are extensively used in engineering practices. However, there exist some controversies in deformation behaviour between polycrystalline tungsten and its bulk counterpart. In this work, elastic modulus, hardness and removal characteristics of polycrystalline tungsten (poly-W) were investigated by use of nanoindentation and nanoscratch. Atomic Force microscopy (AFM) and Scanning Electron Microscopy (SEM) were employed to characterize the surfaces prior to and after indenting/scratching. The elastic modulus and hardness of the poly-W obtained were 323.6 and 7.1 GPa, respectively. Elastic recovery was barely observed in poly-W after indenting and scratching, indicating that the material was dominantly deformed in plastic regime. The plastic deformation of the poly-W was found to be somehow different from the bulk W, but similar to that of single crystal W nanowhiskers. In multi-scratch test, the pitch distance and scratching speed demonstrated to affect the roughness of the scratched surfaces.

Abstract: As limited results were reported in terms of the evolution of sliding friction with growth of oxide layer in thickness during running-in, a pin-on-disc wear test was carried out in this study. 4.8Ni-1.5Cr cast iron as core layer and low carbon steel as outer layers, were thermo-mechanically processed via three different routes. For samples with lower hardness due to their predominantly austenitic or martensite retarded matrices, we found that initially rapid increase of thickness of oxide layer continually lowers the sliding friction. However, after the oxide layer was beyond a certain thickness, the sliding friction began to increase consecutively. After a fluctuation of friction caused by the break-down of oxide, a mild equilibrium wear with roughly constant friction followed.

Abstract: In the present investigation, both micro-crystalline and nanocrystalline diamond (MCD and NCD) films are fabricated, which are characterized by FESEM (Field Emission Scanning Electron Microscopy), surface profilemeter, Raman spectroscopy and Rockwell hardness tester. Moreover, under the dry environment, the frictional behavior of both the films sliding against commonly-used materials in the metal drawing industry is studied on a ball-on-plate rotational frictional tester, including the stainless steel, low-carbon steel, high-carbon steel and copper, demonstrating that the frictional coefficients between NCD films and all these materials are relatively smaller. Furthermore, the wear rates of both the films, which are hardly measured in the ball-on-plate friction tests, are evaluated using a home-made inner-hole line drawing apparatus, with both the diamond films deposited on the inner-hole surfaces and the low-carbon steel wires as the counterparts. Inversely, the NCD films present higher wear rates than the MCD ones, which can be attributed to the deteriorative film purity and adhesion.

Abstract: This investigation attempts to improve the wear resistance of low chromium white cast iron (LCCI) by thermomechanical treatment. The thermomechanical treatment of the brittle LCCI with crack-free was successfully carried out by bonding it with a ductile low carbon steel firstly. Afterwards the dry sliding wear behavior of as-cast (LCCI-A) and thermomechanically processed (LCCI-B) samples was studied using a pin-on-disc apparatus under different test conditions. The microstructural examination shows that the refined supercooled austenite and plenty of secondary carbides in LCCI-B replaced the original microstructure of martensite and retained austenite with network carbide in LCCI-A. This significant evolution is beneficial to form and stabilise the oxide layer on the substrate, which makes the oxidational wear rather than abrasive wear or delamination dominating the wear process so that the improvement of the wear resistance of LCCI was achieved by hot working.