Zhi Jian Peng

Bending Strength of Ceramics Implanted by Titanium, Zirconium and Chromium Ions with MEVVA Source

ZTA (alumina toughened by 20 wt.% zirconia), hot-pressed silicon nitride (with totally 10 wt.% Y2O3 and Al2O3 as additives) and TZP (pressureless-sintered yttria stabilized zirconia) ceramics were implanted by various doses (5 × 1016 ions/cm2 ~ 1 × 1018 ions/cm2) of Ti, Zr, and Cr ions with a MEVVA (metal vapor vacuum arc) source implanter. The bending strength of these ceramics was investigated. It was discovered that, for different ceramics, different behaviors were presented with the same doses of implantation ions. For alumina and zirconia ceramics, the bending strength increased with increasing implantation doses of Ti and Zr ions, but decreased with high dose of Cr ions. For silicon nitride ceramics, however, the bending strength originally increased with smaller doses of metals implanted, and decreased with higher doses of metals of Ti, Zr, and Cr ions. The different behaviors are correlated to the different variations in compositions and microstructures of ceramics after ion implantation.

Indentation Size Effect in the Nanohardness of Soda-Lime Glass

The nanoindentation load-displacement curves of soda-lime glass were analyzed with the widely adopted Oliver-Pharr method. The resultant nanohardness exhibits a significant indentation size effect (ISE). An empirical relationship between the peak load and the contact depth, which was established to analyze the ISE in microhardness tests, was suggested to be suitable for describing the load-dependence of the nanohardness. By comparing the best-fit values of the parameters included in this empirical relationship, the origin of the load-dependence of nanohardness was analyzed briefly.

Characterization of Superhard Ternary (Ti,Al)N Coatings Prepared by Pulsed High Energy Density Plasma

Traditional TiN coatings cannot meet the requirements in many applications under extreme conditions because of their relatively low hardness (similar to2000Hv), high friction coefficient (>0.4), inade- quate thermal stability and insufficient corrosion. (Ti,Al)N coatings are a promising alternative to TiN coatings, which have recently been obtained by some groups. However, The deposition of coatings on ceramic substrates prepared by traditional physical vapor deposition was puzzled by low adhesions. In this work, (Ti,Al)N deposition was realized by a new technique namely pulsed high energy density plasma. The ratio of Ti and Al atoms was kept constant at 1:1, since this was known to be the best ratio for (Ti,Al)N synthesis. However, the process allows many other deposition parameters to be varied. In this study, the influences of the discharge voltage between the inner and outer electrode, the distance between the sample and the pulsed plasma gun, and the shot number of the pulsed plasma on coating formation and properties were investigated. Under the optimum deposition conditions, the adhesive strength of (Ti,Al)N coating to Si3N4 ceramic substrate was satisfactory with the critical load up to more than 80 mN. In addition, the coatings were investigated with respect to mechanical and wear behavior, including nanohardness, Youngs modulus and cutting performances. The (Ti,Al)N coatings possess resulted very high values of nanohardness and Youngs modulus, which are near to 40 GPa and 680 GPa, respectively. Because of the deposition of (Ti,Al)N coatings the wear resistance and edge life of the coated tools were improved dramatically evaluated by the cutting perforinances of the coated tools in turning HT250 (HB230) steel under industrial conditions. These improvements were attributed to a combination of four effects of deposition, ion implantation, quench and solid solution strengthening in terms of the structural analyses.

Description of the Nanoindentation Unloading Behavior of Brittle Ceramics with a Modified Surface

The nanoindentation unloading behavior of some brittle ceramics with modified surfaces was analyzed. It was found that the unloading data may be described well with a quadratic polynomial. The physical meaning of the quadratic polynomial in describing the nanoindentation unloading behavior was then discussed by considering the effect of residual contact stress on the force-displacement relationship. It was suggested that the quadratic polynomial may be considered as a modified form of the basic forcedisplacement relationship for the contact of an isotropic elastic half-space by a rigid conical punch.

Study on the Properties of Alumina Ceramics after Implanted by Titanium Ions with MEVVA Sources

HIP (hot isostatic pressed) high-purity alumina was modified by Ti-ion implantation in a MEVVA (Metal Vapor Vacuum Arc) implanter. The samples were implanted by Ti ions with nominal doses 5×1016 to 1×1018 ions/cm2 under ambient temperature. The effects of titanium implantation and the ion dose implanted on the microstructures and mechanical properties of the ceramics were studied. After implanted by Ti ions, the maximum nanohardness of the as-implanted ceramics were increased about 20%; the bending strength were increased about 22%; the life of the alumina cutting tools were about 2 times longer than before. The result showed that all the factors of the improvement of the ceramic surface states played an important role on the mechanical properties after implantation.

Structure of the Coatings onto Ceramic Cutting Tools Deposited by Pulsed High Energy Density Plasma

With a newly-developed technique, pulsed high energy density plasma (PHEDP), TiN, TiCN, and (Ti,Al)N coatings were deposited onto silicon nitride and cemented carbide cutting tools. The structures of these coatings were systematically investigated in this paper. The average surface roughness (Ra) of the coated tools were ranged in 20~150 nm. The smooth surface of coated tools means that the coatings are promising candidate for cutting tools of high precision and it is in favor of reducing the fiction coefficients and flank wear of tools. The coating thickness varied, in the range of 3~20 µm, with the deposition conditions of the shot number of pulsed plasma, and the voltages between the inner and outer electrodes of the coaxial gun. The coating has a densified structure compared to the substrate structure and almost no pores and cracks exist in the coating surface. The grain sizes of the coating were small (<100nm), much finer than those of the substrate (>2 µm). Except for TiN-Si3N4 system, no apparent columnar grain structure as presented predominantly in typical vapor deposited coatings was observed. In fact, an equiaxed structure was presented, due to the pulsed mode of plasma bombardment and solid solution strengthening of C or Al into TiN lattices, resulting in disruption, through renucleation, of epitaxy on individual columns. A continuous and densified interface was observed. All these characteristics in structures promised an excellent performance of the coated tools.

Description of Unloading Behavior of Berkovich Nanoindentation

We established a new expression to describe the nanoindentation unloading data by assuming that the Berkovich indenter behaves as a conical punch, rather than a paraboloid punch, and properly considering the effect of residual contact stress on the unloading load-displacement relation. The validity of this new approach was confirmed by analyzing the experimental data obtained for a series of brittle materials. It was shown that, compared with the generally adopted power law, this new expression has much clearer physical significance.

Ti(C,N) Hard Coatings Prepared by Pulsed High Energy Density Plasma

A new technique, namely pulsed high energy density plasma, has been developed to deposit hard coating of metals and various compound materials on ceramic and metal substrates. In this system, the plasma density was in the range of 10(14)-10(16) cm(-3) in the glow discharge space; the electron temperature was in the range of 10(5)-10(6) K; the power density was varied from 10 5 to 101 W(.)cm(-2); the pulse width is about 60 mus and the pulse frequency is 10(-2) s(-1). In this study, Ti(C,N) hard coatings were deposited on Si3N4 ceramic cutting tool substrates at room temperature, resulting coatings with high hardness and excellent adhesion to the substrates. The adhesion force of the Ti(C,N) coatings is in the range of 80-100 mN measured by nanoscratch tests, and the nanohardness of the coatings varied from 40 GPa to 50 GPa as measured by a nanoindenter. The tribological properties and the cutting performances of the coated tools were evaluated by turning HT 250 (HB230) steel under industrial conditions. The wear resistance and edge life of the tools were improved dramatically because of the deposition of Ti(C,N) coatings. From the structural analyses, these improvements were attributed to a combination of three effects: deposition, ion implantation and quenching.