The monoclinicetetragond phase transition in ZrO, single crystals was studied at temperature by transmission optical microscopy and X-ray diffraction techniques. A series of timelapse photographs illustrated the relations between the events that occur during the transition. The events themselves were recognized by direct observation using a high-temperature microscope stage and by scrutiny of several high-temperature Laue photographs. During heating the monoclinic phase transforms to the tetragonal by the motion of an interface parallel to the (loo), plane; simultaneous twinning also occurs behind the advanciqg interface. The tetragonal phase is usually twinned on the (112)bcl or (112)bcl plane, and the extent of twinning is influenced by the heating rate. Cooling transforms the untwinned tetragonal form into a twinned monoclinic form with the orientation of the monoclinic twins parallel to the trace of the (Ool), plane when observations are made in the (lOOX, plane. Transformation of a twinned tetragonal crystal results in twins on the { 110}, and { OOl}, planes. Orientation relations in the ZrO, transformation are: (lOO),~~(llO)~c~, [010]~~)[001]bc~, and by the virtue of twinning, (lOo),~l(llO)t,ct, [OOl],ll[OOl]bct. During cooling the same topotaxial relations are maintained.
The technology of brazing a single layer of abrasive on to the surface of a grinding tool, metal single layer (MSL) technology, provides an alternative way to make use of the superabrasives diamond and cubic boron nitride in machining ceramic materials or superalloys, cutting of construction materials, etc. For certain applications of MSL bonded wheels, the grinding or cutting process is very abrasive and the wear resistance of the braze alloy often dominates the wheel failure. The wear resistance of the braze alloy typically used for MSL can be improved by incorporating hard dispersoids. The present study examines the effect of particulate molybdenum, tungsten, SiC, WC, and TiC dispersoids on the wear resistance of Cu–Sn–Ti active braze alloys. Among these, TiC was identified as most effective in enhancing the abrasive resistance of the braze alloy. It was found that a braze alloy of 75 Cu–25Sn–12·5Ti–7·5Zr–10TiC–0·2C (by weight) exhibits high wear-resistance and excellent performance in cutting tests on green concrete.
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