Jianjun Cui

Planar defects and dislocations in HPHT as-grown diamond crystals

In the present paper, diamond crystals approximately 0.8 mm in dimension were synthesized at high temperature and high pressure (HPHT) in the presence of FeNi catalyst in the diamond stable region. An argon beam-milling machine thinned the HPHT as-grown diamonds until they were suitable for examination by cross-sectional transmission electron microscopy (TEM). It was shown that there are a number of twins, stacking faults and dislocation networks on (111) planes in the HPHT-grown diamond crystals. During the diamond growth at HPHT, the growing diamond inevitably traps impurities. Dislocation networks near the zone relieve the concentration stresses caused by the impurity-enriched zones. Twins may be formed mainly due to the carbon atoms falling by mistake into positions where a twin crystal can form during diamond growth. Another possibility for twin formation in the HPHT as-grown diamonds is that twins are initially formed during the nucleation process as in CVD diamonds. Moire images reveal that the density of stacking faults is high. The stacking faults may be formed mainly due to rapid growth of the diamond at HPHT. Another possibility for stacking faults formation is related to the condensation of supersaturated vacancies in the HPHT as-grown diamonds on the (111) plane during rapid quenching after diamond synthesis. The terminating of stacking faults on intersecting twins by moire image suggests that the bordering partial has propagated by glide up to the twin interface during diamond growth, this may be described by the reaction of Shockley partial dislocation with a twin on the (111) plane.

Transmission electron microscopic study of some inclusions in synthetic diamond crystals

Abstract Diamonds synthesized under a high temperature of 1570 K and a high pressure of 5.5 GPa in the presence of FeNi catalyst contain inclusions related to the graphite and the metallic catalyst. Several kinds of inclusions contained in the synthetic diamond were for the first time successfully identified by transmission electron microscopy (TEM). The inclusions trapped in the diamond crystals consist of amorphous graphite, face-centered cubic SiC and face-centered cubic (FeNi) 23 C 6 .

Effect of Micro-Addition Rare Earth and Chrome on Friction and Wear Behavior of Boronized Layer

Application of powder boronizing to mechanical industry has been restricted because of the brittleness of boronized layer, which inevitably leads to decrease of service life of boronized parts. Therefore, attention should be paid to reducing the brittleness of boronized layer without decreasing its high hardness. In the present paper, a study on the effect of micro-addition rare earth and chrome on friction and wear behavior of boronized layer was carried out using an MM-200 wear test machine. Compared with that of pure single Fe2B phase, the brittleness of the boronized layer containing minim rare earth and chrome elements, obtained by powder RE-chrome-boronizing, is reduced, which results in increasing the bearing capacity and wear resistance of the boronized layer. The friction and wear mechanism is also briefly analyzed.

Investigation on defects in HPHT-grown diamond single crystals

In the diamond single crystals synthesized at high temperature and high pressure using FeNi as catalyst, there are usually supersaturated vacancies and inclusions formed during the diamond crystal growth and rapid cooling from high temperature. Some defects such as prismatic dislocation loops, stacking faults and array of dislocations are closely related to such supersaturated vacancies and inclusions. The supersaturated vacancies agglomerate into discs on the (111) close-packed planes, subsequent collapse of the discs forms the dislocation loops and stacking faults. The thermal internal stresses, which are caused by the difference of thermal contraction between the diamond and the inclusions due to the difference of thermal coefficients between them as the diamond is cooled from high temperature, may be relieved by the formation of array of dislocations. In the present paper, these defects in the diamond single crystals were directly examined by transmission electron microscopy (TEM). The characteristics and formation process of these defects were analyzed briefly.