The present work is focused on investigating the effect of SiC addition (0, 15, 20, 25 and 30 vol.%) on microstructural features, phase evolution and mechanical properties of the vacuum hot pressed TiB 2 at 1850 °C/2 h/20 MPa. Hardness measurements revealed an initial increase in hardness from 14.2 GPa for nominally pure TiB 2 to 20.8 GPa for TiB 2 –15 vol.% SiC and a subsequent decrease with further increase in the SiC addition. Also the TiB 2 –30 vol.% SiC showed an improved indentation fracture toughness of 5.76 MPa m 1/2 which was mostly attributed to the addition of the SiC particles that could activate toughening mechanisms such as crack deflection, crack branching and grain breaking. The microstructure of the sintered samples was characterized by XRD and FESEM, which indicated that SiC reacted with and removed oxide impurities (TiO 2 and B 2 O 3 ) that were present on the particle surfaces. Elimination of such impurities promoted densification by minimizing grain coarsening and in composite contain 30 vol.% SiC the reaction led to in situ formation of TiC. Hence, the results indicated that sinterability of TiB 2 -based composites was remarkably improved by addition of SiC compared to the single phase TiB 2 ceramic.

Microstructural development and mechanical properties of hot pressed SiC reinforced TiB2 based composite

The paper is the first of two dealing with the use of ceramic tool materials for the machining of nickel based alloys. While the second contribution presents the results of detailed machinability tests, involving a cross-section of current nitride, superhard and whisker reinforced ceramic tooling products, this first paper comprehensively reviews existing literature on the subject. Following an assessment of tool wear characteristics, such as depth-of-cut notching and the underlying mechanisms involved, in particular the effects of applied mechanical stress and high interface temperatures, details are given of the composition, structure, physical properties and cutting performance of various state-of-the-art ceramic tool materials. Although only recently available commercially, whisker reinforced composite tools, comprising an alumina matrix with approximately 25% by volume silicon carbide whiskers, are reported to be capable of operating at cutting speeds up to 750 m/min on some nickel based alloys.

Use of ceramic tools for machining nickel based alloys

TiB2–SiC ceramic composites, with different contents of SiC whiskers (SiCw), as a ceramic sinter-additive, were prepared by the hot pressing process at 1850 °C for 2 h under a pressure of 20 MPa. For comparison, a monolithic TiB2 ceramic was also fabricated under the identical temperature, pressure, atmosphere, and holding time by the hot pressing process. The effects of fabrication process and SiC whiskers on microstructural features, phase evolution and mechanical properties were investigated. Hardness measurements revealed an initial increase in hardness for TiB2–SiC compared to TiB2. Also the improvement of the fracture toughness was attributed to the toughening and strengthening effects of SiC whiskers such as crack deflection. The results showed that promoted densification of TiB2–SiC ceramic composites is due to addition of SiC whiskers and reduction of oxide impurities by reacting with SiC whiskers and removing them from the surface layer of TiB2 particles. The reaction between TiB2 particles and SiC whiskers led to in-situ formation of TiC phase in the matrix as well. In general, it is concluded that the sinterability of TiB2-based composites was remarkably improved by introducing SiC whiskers compared to the single phase TiB2 ceramic.

Characterization of hot pressed SiC whisker reinforced TiB2 based composites

An Al2O3-based composite ceramic tool material reinforced with WC microparticles and TiC nanoparticles was fabricated by using hot-pressing technique. The cutting performance, failure modes and mechanisms of the Al2O3/WC/TiC ceramic tool were investigated via continuous and intermittent turning of hardened AISI 1045 steel in comparison with those of an Al2O3/(W, Ti)C ceramic tool SG-4 and a cemented carbide tool YS8. Worn and fractured surfaces of the cutting tools were characterized by scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS). The results of continuous turning revealed that tool lifetime of the Al2O3/WC/TiC ceramic tool was higher than that of the SG-4 and YS8 tools at all the tested cutting speeds. As for the intermittent turning, tool life of the Al2O3/WC/TiC ceramic tool was equivalent to that of YS8, but shorter than that of the SG-4 at lower cutting speed (110 m/min). However, tool life of the Al2O3/WC/TiC ceramic tool increased when the cutting speed increased to 170 m/min, becoming much longer than that of the SG-4 and YS8 tools. The longer tool life of the Al2O3/WC/TiC composite ceramic tool was attributed to its synergistic strengthening/toughening mechanisms induced by the WC microparticles and TiC nanoparticles.

Cutting performance and failure mechanisms of an Al2O3/WC/TiC micro- nano-composite ceramic tool

The disclosed is an ultra-hard composite material. The method for manufacturing the ultra-hard composite material includes mixing a metal carbide powder and a multi-element high-entropy alloy powder to form a mixture, green compacting the mixture, and sintering the mixture to form the ultra-hard composite material. The described multi-element high-entropy alloy consists of five to eleven principal elements, with every principal element occupying a 5 to 35 molar percentage of the alloy.

Ultra-hard composite material and method for manufacturing the same

Physical properties and cutting performance of silicon nitride ceramic

PROBLEM TO BE SOLVED: To provide a sintered MnCu-based high-damping alloy with an optional shape of a twin crystal type high Mn composition by sintering at a temperature lower than the casting temperature of an MnCu-based high-damping alloy since the Mn composition of an MnCu-based high-damping alloy capable of being cast is limited by the conventional casting method. SOLUTION: The MnCu-based high-damping alloy is mainly made up of Mn, Cu and Ni, and contains one or more elements selected from Bi, Si, Sn and B as a liquid phase sintering assistant(s), and when containing Bi, the content of Mn is COPYRIGHT: (C)2010,JPO&INPIT

MnCu-BASED HIGH-DAMPING ALLOY

PROBLEM TO BE SOLVED: To provide a sintered MnCu based high damping alloy with an optional shape having a twin crystal type high Mn composition by sintering at a temperature lower than the casting temperature of an MnCu based high damping alloy. SOLUTION: Regarding the sintered high damping alloy, in a manganese-copper-nickel-bismuth based sintered alloy obtained by adding alloy powder composed of a ternary system of, by weight, 67 to 94% manganese, 6 to 33% copper and 2 to 15% nickel with Bi in the group V B as a sintering assistant by 0.5 to 30 wt.% and performing sintering by a liquid phase sintering method and having a relative density of 70 to 100%, in the temperature range of -50 to +300°C, to the frequency region of 0.5 to 100 Hz, logarithmic attenuation factor is 0.01 to 1. COPYRIGHT: (C)2006,JPO&NCIPI

Fukazawa Kenji

Papers

Physical properties and cutting performance of silicon nitride ceramic

MnCu-BASED HIGH-DAMPING ALLOY

Manganese-copper-nickel-bismuth based sintered high damping alloy

Silicon nitride sintered body for tool