Zhijian Peng

On the description of indentation size effect in hardness testing for ceramics: Analysis of the nanoindentation data

Abstract The nanoindentation hardnesses of a commercially available soda-lime glass, a tetragonal ZrO 2 polycrystalline and a hot-pressed Si 3 N 4 were measured in the peak load range from 7.5 to 500 mN. The experimental results revealed that, for each material, the measured hardness exhibits a peak-load- dependence, i.e., indentation size effect (ISE). Such a peak-load-dependence was then analyzed using the Meyer’ law, the Hay–Kendall approach, the proportional specimen resistance (PSR) model, the elastic recovery model and the modified PSR model. The analyses revealed that: (1) Meyers law provides a satisfactory description for the experimental data for each material but cannot provide any knowledge of the origin of the observed ISE; (2) the Hays–Kendall approach, the elastic recovery model and the PSR model yield meaningless values of the parameters included in the corresponding equations, invalidating the applicability of these models in analyzing the ISE in the nanoindentation region; (3) the modified PSR model is sufficient for describing the observed ISE but the physical meaning of this model seems to be more complex than those proposed originally. For each material, the true hardness was also determined based on the PSR model, the elastic recovery model and the modified PSR model, respectively. It was found that the true hardness values deduced based on different models are similar with each other and this similarity was attributed to the similarity between the empirical equations adopted in these models.

Hard and wear-resistant titanium nitride coatings for cemented carbide cutting tools by pulsed high energy density plasma

Abstract Hard and wear-resistant titanium nitride coatings were deposited by pulsed high energy density plasma technique on cemented carbide cutting tools at ambient temperature. The coating thickness was measured by an optical profiler and surface Auger microprobe. The elemental and phase compositions and distribution of the coatings were determined by Auger microprobe, x-photon electron spectroscope, and X-ray diffractometer. The microstructures of the coatings were observed by scanning electron microscope and the roughness of the sample surface was measured by an optical profiler. The mechanical properties of the coatings were determined by nanoindentation and nanoscratch tests. The tribological properties were evaluated by the cutting performances of the coated tools applied in turning hardened CrWMn steel under industrial conditions. The structural and mechanical properties of the coatings were found to depend strongly on deposition conditions. Under optimized deposition conditions, the adhesive strength of TiN film to the substrate was satisfactory with the highest critical load up to more than 90 mN. The TiN films possess very high values of nanohardness and Young’s modulus, which are near to 27 GPa and 450 GPa, respectively. The wear resistance and edge life of the cemented carbide tools were improved dramatically because of the deposition of titanium nitride coatings.

Hard and wear-resistant titanium nitride films for ceramic cutting tools by pulsed high energy density plasma

High-quality and wear-resistant titanium nitride films were deposited onto silicon nitride ceramic cutting tools by pulsed high energy density plasma technique at ambient temperature. The adhesive strength of TiN film to the ceramic substrate has been satisfactory with very high critical load up to more than 80 mN measured by nanoscratch tester. The TiN films possess very high values of nanohardness and Youngs modulus, which are near to 28 and 350 GPa, respectively. The wear resistance and edge life of the ceramic tools were increased greatly because of the deposition of titanium nitride coatings. The cutting performance of the silicon nitride ceramic tools with such TiN films could be optimized by varying the deposition conditions, including the (shot) number of pulsed plasma and the discharge voltage between the inner and outer electrodes, etc.

Effect of peak load on the determination of hardness and Young's modulus of hot-pressed Si3N4 by nanoindentation

Abstract The indentation load–displacement curves of a hot-pressed silicon nitride were measured under different peak load levels. The unloading segments of these curves were analyzed using the widely adopted Oliver–Pharr method. It was found that both the hardness, H , and the Youngs modulus, E , exhibit significant peak-load-dependence. Empirical approaches were then proposed to determine the load-independent hardness and modulus. The hardness and modulus deduced from these empirical approaches were proven to be comparable with the literature reported data measured with conventional methods.

A new function for the description of the nanoindentation unloading data

Abstract A new function was proposed for describing the nanoindentation unloading data. The initial unloading slope determined based on this new function is in good agreement with the widely adopted power-law relation. However, the physical significance of the new function is much clearer than that of the power-law.

Microstructure and mechanical properties of titanium nitride coatings for cemented carbide cutting tools by pulsed high energy density plasma

Hard, wear-resistant and well-adhesive titanium nitride coatings on cemented carbide cutting tools were prepared by the pulsed high energy density plasma technique at ambient temperature. The results of Auger spectra analysis indicated that the interface between the coating and substrate was more than 250 nm. Under optimized deposition conditions, the highest critical load measured by nanoscratch tester was more than 90 mN, which meant that the TiN film was well adhesive to the substrate; the highest nanohardness and Young’s modulus according to nanoindentation tests were near to 27 and 450 GPa. The results of cutting tests evaluated by turning hardened CrWMn steel in industrial conditions indicated that the wear resistance and edge life of the cemented carbide tools were enhanced dramatically because of the deposition of titanium nitride coatings. These improvements were attributed to the three combined effects: the deposition and ion implantation of the pulsed plasma and the becoming finer of the grain sizes.

Preparation of epitaxial Y1-xHoxBa2Cu3O7-δ high Tc films on (100)Zr(Y)O2 substrates

Abstracts are not published in this journal

The relationship of the critical current density and the lattice deformation in Y1−xRExBa2Cu3O7−δ epitaxial films

Abstract The critical current densities Jc of Y 1−x RE x Ba 2 Cu 3 O 7−δ (RE=Ho, Dy and Eu) epitaxial thin films with x=0,0.2,0.4,0.7,1.0 at various temperatures and magnetic fields have been measured magnetically. XRD results showed that the more serious the lattice deformation, the higher the Jc of the films becomes, have been observed by the width of the X-ray reflections. These results demonstrated the stress field pinning induced by the lattice deformation in RE-doped Y 1−x RE x Ba 2 Cu 3 O 7−δ epitaxial thin films.