Jiuhua Xu

Optimization design of grinding wheel topography for high efficiency grinding

Abstract In view of the limitation of prior topography models of the grinding wheel, a new method for optimization design of grinding wheel topography is advanced. The optimization model can be used to optimize the topography in accordance with machining demands and grinding parameters as well as optimize grinding parameters in accordance with the topography and machining demands. Furthermore, a superabrasive slotted grinding wheel is designed as a practical application of the optimization model and a creep-feed deep grinding experiment is carried out to verify the optimization results.

Interfacial reaction between cubic boron nitride and Ti during active brazing

Thermodynamic and reaction process analyses were performed to understand the joining characteristic during high temperature brazing between cubic boron nitride (CBN) grit and a silver-base filler alloy containing Ti as an active element. Experimental information on the microstructure of the brazed joint, the composition of the interface, and the shape of the compounds formed on the surface of the grit was obtained by scanning electron microscopy, energy-dispersive x-ray, and x-ray diffraction. The results indicate that Ti in the molten filler alloy facilitated good wetting between the solid CBN crystals and braze filler alloy. The transition layer formed by the interaction of TiN and TiB2 was one of the key factors in joining the CBN and steel substrate.

Thermodynamic and kinetic analysis of interfacial reaction between CBN and titanium activated Ag–Cu alloy

Abstract Thermodynamic and kinetic analysis was performed in order to study the interfacial reaction mechanism of cubic boron nitride (CBN) abrasive grains and Ti activated Ag–Cu filler alloy during high temperature brazing. Meanwhile, microstructure of the interfacial layer was experimentally detected using scanning electron microscope (SEM), energy dispersion spectrometer (EDS) and X-ray diffraction (XRD) in the present paper. The results indicate that according to the thermodynamic theory, the interfacial reaction has been proved feasible, and during brazing the special active element Ti concentrated to and reacted with the CBN abrasive to form TiB2 and TiN, which joined hard the abrasive grain and steel substrate. Furthermore, the diffusion activation energy of the growing process in the interfacial reaction layer has discovered that the layer growth largely depends on the new formed TiN under conditions of 1153–1193 K and 5–30 min.

Role of Al additions in wear control of nanocrystalline Mo(Si1−xAlx)2 coatings prepared by double cathode glow discharge technique

Abstract Four kinds of nanocrystalline Mo(Si1−xAlx)2 coatings with differing Al contents are prepared onto a Ti–6Al–4V substrates by a double cathode glow discharge apparatus. The microstructural features of the deposited coatings were characterised by X-ray diffraction, scanning electron microscopy and transmission electron microscopy. These coatings are composed of the equiaxed C40–MoSi2 grains with the average grain size of ∼5 nm. Nano-indentation measurements indicated that the hardness H, elastic modulus E and the H/E or H3/E2 ratio of the nanocrystalline Mo(Si1−xAlx)2 coatings slightly increase with the increase in Al content. The tribological behaviour of the nanocrystalline Mo(Si1−xAlx)2 coating sliding against a ZrO2 ceramic ball at room temperature has been compared using a ball-on-disc type tribometer under unlubricated conditions. Experimental results showed that the specific wear rates of the nanocrystalline Mo(Si1−xAlx)2 coatings decrease with increasing Al content and are dramatically reduced by more than 1–2 orders of magnitude over the uncoated Ti–6A1–4V. The enhancement of wear resistance of the nanocrystalline Mo(Si1−xAlx)2 coatings by Al additions is correlated with the increased mechanical properties and the forming oxide layer by tribochemical reactions.

Microstructure characteristics of CBN/steel joints brazed with TiB2 modified active filler

Abstract The joint of cubic boron nitride (CBN) grits to 0·45%C steel were obtained by using TiB2 modified Ag–Cu–Ti active filler at the brazing temperature of 920°C for the holding time of 5 min. The microstructure characteristics of the brazing interface were detected by means of optical microscope, scanning electron microscope, energy dispersion spectrometer, X-ray diffraction and microhardness measuring equipment as well. It has been found that the microstructure of Ag–Cu–Ti filler layer is significantly refined by TiB2 particles. The almost well proportioned distribution of TiB2 particles in the filler layer is realised. Negative influence of TiB2 particles has not occurred on the chemical reaction of CBN particles and the filler at elevated temperatures. Reliable joining of CBN grits to 0·45%C steel is accomplished dependent on the resultant reaction products at the brazing interface.

Experimental study on the milling of a Ti Beta 21S

Abstract Ti Beta 21S is a new metastable beta titanium alloy which is generally known to be one of the most difficult materials to machine because of its high hardness, high strength at high temperature, affinity to react with the tool materials, and low thermal diffusivity. In this paper, the tool wear and cutting force in the milling process were studied by experiment together with machinablity assessment when using different cutting tools. The optimized machining parameters are provided for reference to actual production.

Effect of Al-5Ti-1B-1Re on the Microstructure and Hot Crack of As-Cast Al-Zn-Mg-Cu Alloy

High crack tendency is easy to occur during preparation of the castings and ingots of Al-Zn-Mg-Cu alloy, and it is most difficult to be solved due to the characteristics for the series alloy. As-cast microstructures and hot cracking tendency of Al-Zn-Mg-Cu alloy with different addition levels of Al-5Ti-1B-1Re were investigated in the paper. Moreover, solidification characteristics of the experimental alloys with different mass fractions of Al-5Ti-1B-1Re were analyzed, and the addition content of Al-5Ti-1B-1Re was optimized. These results indicate that the microstructure of the experimental alloys with Al-5Ti-1B-1Re refiner is fine obviously, the dendrite shape refined by Al-5Ti-1B-1Re becomes more globular, the grain boundary is smoother, and the SDAS is smaller compared with the alloy without Al-5Ti-1B-1Re. When the addition level of the grain refiner is less than 0.2%, the hot cracking tendency for the experimental alloy is reduced. The addition of 0.2% Al-5Ti-1B-1Re is best effective to improve the as-cast microstructures and hot cracking of Al-Zn-Mg-Cu alloy, and the best addition level of Al-5Ti-1B-1Re refiner is 0.2%.

Comparative investigation on wear behavior and self-sharpening phenomenon of polycrystalline cubic boron nitride and monocrystalline cubic boron nitride grains in high-speed grinding

High-speed grinding experiments were conducted on a nickel-based superalloy Inconel718 with the monolayer brazed wheel containing monocrystalline cubic boron nitride grains and polycrystalline cubic boron nitride grains. Comparative investigation on the wear behavior and self-sharpening phenomenon of polycrystalline cubic boron nitride and monocrystalline cubic boron nitride grains was carried out based on the fractal analysis. The results obtained indicate that the wear process of the monocrystalline cubic boron nitride grain cutting edges is, in order, attritious wear → large fracture → micro fracture → large fracture → attritious wear, while that of the polycrystalline cubic boron nitride grain cutting edges is micro fracture → attritious wear → micro fracture. Micro fracture of polycrystalline cubic boron nitride grain occurs easily in the particular zone where large impact load is formed due to the first contact between the grain cutting edges and the workpiece material. The fractal dimension of monocrystalline cubic boron nitride wheel is 2.040–2.047, while that of the polycrystalline cubic boron nitride wheel is 2.049–2.054, which indicates that the polycrystalline cubic boron nitride grain cutting edges are finer than that of the monocrystalline cubic boron nitride counterparts. Compared to monocrystalline cubic boron nitride grains, better performance, that is, smaller radial wheel wear, lower grinding force and forces ratio, is obtained for polycrystalline cubic boron nitride grains due to micro fracture behavior and self-sharpening phenomenon in high-speed grinding.

Comparative study on cutting behavior of vitrified cubic boron nitride wheel and electroplated cubic boron nitride wheel in high-speed grinding of (TiCp + TiBw)/Ti-6Al-4V composites

High-speed grinding experiments of particle reinforcing titanium matrix composites ((TiCp + TiBw)/Ti-6Al-4V) were carried out with vitrified cubic boron nitride wheel and electroplated cubic boron nitride wheel, at the wheel speed ranged from 80 to 140 m/s. The cutting behavior, that is, grinding force, grinding temperature, specific grinding energy, and ground surface morphology, and grinding chips are analyzed. The results indicate that compared to the workpiece speed and the depth of cut, the wheel speed has a more significant influence on the grinding forces. The grinding temperature and specific grinding energy obtained with the vitrified cubic boron nitride wheel are always larger than those with the electroplated cubic boron nitride wheel. Based on the comprehensive consideration in terms of grinding force, grinding temperature, and specific grinding energy, the electroplated cubic boron nitride wheel is more suitable than vitrified cubic boron nitride wheel for high-speed grinding particle reinforcing titanium matrix composites. The removal of the reinforcements of particle reinforcing titanium matrix composites is mainly by means of pullout, fracture or crushing, micro-cracks, voids, and smearing. The segment chips containing the reinforcements are formed during high-speed grinding of particle reinforcing titanium matrix composites.

Grinding temperature and wheel wear of porous metal-bonded cubic boron nitride superabrasive wheels in high-efficiency deep grinding

High-efficiency deep grinding experiments of Inconel 718 nickel-based superalloy was carried out with the porous metal-bonded cubic boron nitride superabrasive wheel, in which the uniform and large pores were formed by the broken alumina bubble particles in the working layer after wheel dressing. Grinding temperature, energy partitioning into workpiece, and wheel wear were investigated. Results obtained show that long maintenance of low grinding temperature, that is, 50 °C–170 °C, is obtained in high-efficiency deep grinding with the porous metal-bonded cubic boron nitride wheel. The energy partitioning into the ground workpiece is ranged from 2% to 6%, which is smaller than that with the conventional vitrified cubic boron nitride wheels and alumina abrasive wheels. Sufficient storage space for chips and coolants contributes to the excellent performance of the porous metal-bonded cubic boron nitride wheel in high-efficiency deep grinding. Abrasion wear and grain fracture are the dominant wear patterns of the porous cubic boron nitride wheel in the steady wear stage, while chips loading and grain pullout play a critical role in the final dramatic wear behavior of the porous wheel.