Papers by Author: Shi Yong Liu

Abstract: Two kinds of ceramic additives have been developed that one is the serpentine particles and another is a blend of serpentine particles and catalyst. The tribological properties of the addition of different additives are investigated through a series of friction and wear experiments. Wear surface and the composition of the tribofilm were examined by SEM, EDS and XPS. In case of single serpentine additive, tribo-film can be formed gradually on the worn metal surface. The friction coefficient is about 0.11. The tribofilm mainly consists of Mg and Si elements transferred from the additive. This can compensates part of wear mass loss, avoids the direct contact of the two rubbing surfaces, and thus effectively improves the anti-wear characteristics. In case of the blend oil additive, the tribo-film formed obviously on the worn surface in the initial stage and no obvious film at end of the test. However, the friction coefficient can lower even to 0.007~0.008 compared with the above experiment. The worn surface becomes very smooth. Chemical analysis shows that there is a very thin film of carbon concentration with thickness of 30~50nm on the worn surface. Existence of the very thin carbon-concentrated film and mirror-like surface generates super low friction coefficient.

Abstract: By application of clad-bonding technique of pure copper sheet and plain low carbon steel rebar Q195, the cladding wires in different diameter by drawing at room temperature have been worked. The increasing ratio of the area of grain boundary is in direct proportion to deformation approximately. The resistivity of the cladding wires go up in direct proportion to deformation because the increment of the area of grain boundary results in increment of static disfigurement to electron dispersion. When deformation is less 9.6, the relative increment of resistivity is less 1.1%, i.e. the wire is provided with good electrical conductivity. And the resistance and resistivity of the wires can be estimeted based on copper ratio of transverse section of the cladding wire and the deformation by drawing at room temperature.

Abstract: The microstructure and mechanical properties of pure copper clad Aluminum wires in different diameters by drawing at room temperature were studied in this paper. The results show that the microstructure of the cladding wire by drawing at room temperature is vimineous grain as fibril shape from prime equiaxed grain. The fibril diameter is in inverse proportion to deformation and the fibril length is in direct proportion to square of deformation approximately. The ultimate tensile strength of the cladding wire by drawing at room temperature increases in direct proportion to square root of deformation, and the elongation decreases and fluctuates. Basis of the ultimate tensile strength of prime pure copper and aluminum alloy, the ultimate tensile strength of the cladding wires in different diameters can be doped out by mixed principle of composite material.

Abstract: Fracture surface and crack propagation in low temperature brittle fracture (LTBF) of an 18Cr-18Mn-0.7N high nitrogen austenitic steel (HNAS) were examined by means of scanning electronic microscopy, and compared with behaviours of LTBF of low carbon steel. Similar to BCC low carbon steel, the HNAS experienced a typical ductile-to-brittle transition (DBT) with decreasing temperature, and the appearance of the fracture surface transited from fibrous to granular. Dual-surface observation revealed that there were three types of fracture modes in LTBF of the HNAS: annealing twin boundary fracture, intergranular fracture, and transgranular fracture. The annealing twin boundary fracture facets were parallel to {111} planes, and were fairly flat and smooth, with a pattern of three sets of parallel straight-lines intersecting at 60
. There were also bent steps that originated and terminated at grain boundaries. The transgranular fracture facets were coarse and uneven, with uniformly distributed small pits and partially river pattern on them. The intergranular fracture facets were smoothly curved ones on which more than three sets of parallel deformation structure trace lines were observed. Careful observation on crack propagation demonstrated that during LTBF of the HNAS, microcracks formed firstly at grain boundary and annealing twin boundary, and then these microcracks came together and coalesced to induce crack propagation through grains, resulting in a fracture appearance with shiny facets distributing in dull facets.