Sintering of Ti(C,N)-WC/Mo2C-(Ta,Nb)C-Co/Ni Cermets Investigated by CO and N2 Outgassing

Cermets of the type Ti(C,N)-WC/Mo2C-(Ta,Nb)C-Co/Ni with changing [Mo]/([Mo] + [W]) ratio were subjected to an investigation of outgassing of CO and N2 upon sintering. Quantification of CO and N2 was performed by gas calibration, measurement of masses 12 (12C), 14 (14N) and 28 (28CO and 28N2), as well as C, N, O analysis of the samples before and after sintering. The formation of CO occurs at lower temperatures than that of N2, both gases being completely evolved already at solid-state sintering conditions. If pre-alloyed powders are employed in the starting formulation, the amount of evolved gases is substantially reduced, because part of the formation of mixed hard phases is anticipated. Changing binder composition from Co:Ni = 1:1 to 2:1 and 3:1 does not change the outgassing characteristics, while different batches of nominally the same Ti(C,N) powder can have significant influence. Mass spectrometry is a most valuable in situ tool for getting insight into the metallurgical reactions occurring upon sintering. These reactions result in the typical microstructure and influence the properties of cermets.

Research on the Densification Process of the Mechanically-Alloyed Amorphous 2Si-B-3C-N Powder

A mixture of the commercially available cubic silicon powder, hexagonal boron nitride powder and graphite powder was mechanically alloyed to prepare amorphous 2Si-B-3C-N composite powder. The amorphous powder was heated up to 1900°C in nitrogen, with a heating rate of 20°C/min and under a pressure of 80 MPa. Careful investigation was carried out on the densification curve, the microstructure and the mechanical properties of the prepared ceramics. Results show that the amorphous 2Si-B-3C-N powder mainly consists of near-spherical agglomerates, with an average size of 3.5±2.4 micrometers. When the amorphous powder was hot pressed, the densification process mainly included three stages, the denser packing of powder particles with the help of axial pressure, the initial sintering at about 1500-1800°C, and the rapid sintering at temperatures approximately higher than 1830°C. When the 2Si-B-3C-N ceramic was hot pressed at 1900°C for 10-30 mins, it exhibited large volume shrinkage, noticeable reduction of pores, and significantly improvement of density and mechanical properties. The applied high temperature and large pressure may give rise to severe plastic deformation, viscous flow and creep of powder particles, which greatly contribute to the rapid densification of the amorphous 2Si-B-3C-N powder.

Study on Preparation and MD Simulation of Nano Fe4N

Nano Fe4N powder has been successfully prepared by the combination between high pressure combined method of reduction and nitriding and molecular dynamics (MD) simulation. The phase, composition, morphology, and magnetic properties have been preliminarily characterized by XRD, TEM, and VSM to investigate the influence of temperature, time, ammonia hydrogen ratio, and pressure during reaction process on the preparation. The results indicate that the preferable nano Fe4N powder of the average size around 35[Formula: see text]nm could be obtained nitriding at 0.4[Formula: see text]MPa and 673[Formula: see text]K for 2.5[Formula: see text]hours with the ammonia hydrogen ratio being 3:1. The results of magnetic detection show that the nano Fe4N produced here is a fairly desirable soft magnetic material with Ms[Formula: see text][Formula: see text][Formula: see text]169.70[Formula: see text]emu/g. This process could reduce the reaction temperature and shorten the reaction time, which is of important significance to the industrial production of nano Fe4N powder.

Magnetic Properties of Sm-Fe-N/Co-B Composite Magnets Prepared by Chemical Reduction

An attempt was made to produce Sm-Fe-N/Co-B composite magnets by chemical reduction. It was found that a composite powder consisting of Sm-Fe-N particles coated with fine Co-B particles could be obtained by chemical reduction. The Sm-Fe-N/Co-B composite powder acted as a single hard magnetic phase and showed a smooth hysteresis loop. The composite powder exhibited a higher remanence of 93.1 Am2/kg and a higher coercivity of 0.45 MA/m than a mixture of the Sm-Fe-N powder and Co-B powder prepared by a similar procedure but using a higher concentration of aqueous solution for the chemical reduction.

Optimization of High Energy Ball Milling Parameters for Synthesis of Ti1-xAlxN Powder

Taguchi’s method was applied to investigate the effect of the main HEBM parameters: milling time (MT), ball to powder weight ratio (BPWR) and milling speed (MS) on the dissolved AlN fraction in TiN. The settings of HEBM parameters were determined by using the orthogonal experiments array (OA). The as-received and milled powders were characterized by X-ray diffraction (XRD). The optimum milling parameter combination was determined by using the analysis of signal-to-noise (S/N) ratio. According to the analysis of variance (ANOVA) the milling speed is the most effective parameter and the optimal conditions for powder synthesis are: MT 20h, MS 600rpm, BPWR 50:1. The result of the experiment conducted under optimal conditions (AlN was completely dissolved during experiment) confirmed the conclusions of the statistical analysis.

Sputtering of Titanium in Co-Cr-Mo Alloys for Orthopedic Implant Materials

Sputtering process of titanium have been carried out to improve the hardness and wear resistance of the Co-Cr-Mo alloy for orthopedic implant material. The CoCrMo alloy was synthesized by melting process with addition of Cr2N powder into melts to define the high Cr and high N contents. The solid Ti target was sputtered by argon gas and coated into the CoCrMo substrate at temperature of 200 °C for 2, and 4 hours in the nitrogen gas environment. Characterization was performed to the specimen of CoCrMo ingot before and after sputtering process by microstructure, hardness, corrosion and wear resistance tests. Synthesis of the alloy produced dendrite structure ingot. The hardness, the wear resistance and the corrosion resistance in the simulation body fluid increased after sputtering process due to the formation of oxide thin layer in surface of the alloy.