Effect of HPHT Treatment on Spectroscopic Features of Natural Type Ib-IaA Diamonds Containing Y Centers

In this paper, we report a spectroscopic study of natural type Ib-IaA diamonds containing Y centers subjected to high-pressure high-temperature treatment at 7–7.5 GPa and 1700–2200 °C. Diamond samples showing the Y centers as the dominant absorption feature in the infrared spectra were selected from a collection of natural diamonds from alluvial placers of the northeastern Siberian Platform. The samples were investigated by spectroscopic techniques before and after each annealing stage. It was found that upon annealing at temperatures higher than 2000°C, the defect-induced one-phonon spectra changed from the Y centers to a new form with a characteristic band peaking at 1060 cm−1. Photoluminescence spectra of the samples were modified after each annealing stage starting from 1700 °C. The most significant changes in photoluminescence occurred at temperatures higher than 2000 °C and were associated with a sharp increase of the intensity of an emission band peaking at about 690 nm. A comparison with natural red-luminescing diamonds from Yakutian kimberlite pipes was performed. It was concluded that the observed 1060 cm−1 IR band and the 690 nm red emission band are genetically related to the Y centers and that defects or impurities responsible for the Y centers appear quite widespread in natural diamonds from various deposits worldwide.

COMPARISON STUDY BEWTWEEN THE RECOVERY BEHAVIOR OF DEFORMED QUENCHED, PRE-ANNEALED AND PULSED LASER DAMAGED Fe50Ni50 ALLOY BY MAGNETIC MEASUREMENTS

Through the magnetic measurements, isochronal annealing experiments in the temperature 25950 ºC of deformed, quenched, pre-annealed and pulsed laser damage samples Fe50Ni50 alloy revealed the existence of three annealing stages I, II and III in the annealing spectrum of heavily cold-worked by observing the associated changes in maximum magnetic permeability (µmax) on the magnetic field(H) for different annealing temperature. The first annealing stage I appeared in the temperature range from125-500 ºC and it was activated by energy 1.05 eV. It was attributed to the short range order caused by the long range migration of vacancies. The second annealing stage II appeared in the temperature range from 550-750 ºC and it was activated by 1.82 eV, it is associated with an increase in µmax due to the dissociation of vacancy clusters formed during stage I. The third annealing stage III appeared in the temperature range from 750-825 ºC and it was activated by 3.04 eV, it was related to the climb motion of dislocation during the recrystallization process.

Diffusion of the Carbon Vacancy in a-Cut and c-Cut n-Type 4H-SiС

The diffusion of the carbon vacancy (VC) in n-type 4H-SiC has been studied using Deep Level Transient Spectroscopy (DLTS). Samples grown along two different crystallographic planes, (0001) or c-cut and (11-20) or a-cut, have been utilized. The samples were implanted with 4.0 MeV C ions to generate VC’s and subsequently annealed at temperatures between 200 and 1500 °C. Following each annealing stage, concentration versus depth profiles of the VCwere obtained. The VCis essentially immobile in both the c-cut and a-cut samples up to at least 1200 °C. The 1400 °C annealing stage, however, resulted in considerable migration, predominantly along the a-direction. Using half the difference in the Full Width at Half Maximum (FWHM) of the initial and diffused concentration profiles as a measure of the diffusion length, we deduced the diffusivity of the VCat 1400 °C to be approximately (3.8±1.1)×10-14cm2/s along the c-axis and (4.1±1.2)×10-13cm2/s along the a-axis, indicating a substantial anisotropy for the VCdiffusion in 4H-SiC.

Pearlitic Lamellae Spheroidisation During Austenitization and Subsequent Temperature Hold

Typical processing routes for bearing steels include a soft annealing stage. The purpose of this procedure is to obtain a microstructure containing globular carbides in ferritic matrix. A newly developed process called ASR (Accelerated Spheroidisation and Refinement) cuts the carbide spheroidisation times several fold, producing considerably finer globular carbides than conventional soft annealing. Finer microstructure also leads to more homogeneous and finer structure after final hardening process. The present paper explores process of the accelerated spheroidisation (ASR) in steel 100CrMnSi6-4 with initial pearlitic structure. Cementite lamellae morphology was observed in different stages of austenitization. The heat treatment was performed using induction heating in quenching dilatometer. There was analysed influence of austenitization temperature and austenitization time on spheroidisation. Hardness and carbide morphology was observed. Deep etching was used to reveal evolution of cementitic lamellae fragmentation. It is favourable process especially in induction treatment of small parts.