Li Ming Ke

A Novel Way to Fabricate Carbon Nanotubes Reinforced Copper Matrix Composites by Friction Stir Processing

Carbon nanotubes(CNTs) reinforced copper matrix composites were successfully produced by Friction Stir Processing (FSP). The effect of applying multiple FSP passes on the forming of composites was studied, the microstructure, microhardness and conductivity of the good forming composite were analyzed. The experimental results showed that CNTs uniformly distributed and good forming composite can be obtained by three FSP passes. Compared to the parent material, the grain size of the composite has significantly refined, and the microhardness of the composite has also greatly improved, but the conductivity of the composite has a small decrease.

A novel method for measurement of electronic work function of micro/nanostructure materials using a Kelvin probe system

Work function (WF) can be measured using the Kelvin probe (KP) technique to characterize surface behavior of micro/nanostructures grown on substrates such as metals or semiconductors. However, for such micro/nanostructures, substrates with different WF can strongly affect the measurements if they are exposed directly to face the Kevin probe tip. In this article, a model is proposed to investigate the WF of sparse ZnO nanorods grown on an Si substrate. It is demonstrated that theoretical results from the model are consistent with experimental observations performed using a KP system.

Study on the Microstructure of Micro Laser Welded Joint of TiNi Shape Memory Alloy Sheet

Butt welding of 0.2mm thick TiNi shape memory alloy sheet was successfully realized by using micro impulse laser whose average power is 80W and the microstructure of welded joint was study in this paper. The results show that, the welded joint of micro laser welding can be divided into four zones according to grain size and microstructure. The microstructure in base metal zone is rolled structure and the grains are coarse and heterogeneous. The microstructures of welded seam center zone are fine equiaxed crystals and the microstructures of both lower surface and upper surface edge zone are columnar crystals. There is almost no obvious coarse grain heat-affected zone at the edge between welded seam and base metal. There is obvious segregation layer in local area of welded seam because the content of Ti and Ni elements is changed and different with base metal during the crystallizing course of welding pool.

Microstructure and Corrosion Resistance of AZ80/Al Composite Plate Fabricated by Friction Stir Processing

AZ80/Al composite plate was fabricated by means of friction stir processing (FSP) aimed at the improvement of corrosion resistance of magnesium alloy. The cross-section microstructure, surface morphology and corrosion resistance of the Al composite layer were investigated. The experiment results indicated that a dense composite Al layer with superfine and uniform grains was formed, and a few amount of intermetallic compounds existed in the area of Mg/Al interface. The bonding strength of AZ80 magnesium alloy substrate and 1060 pure Al layer was proved to be high which was resulted from the metallurgical bonding of FSP. Microhardness measurement showed the continuous changing of microhardness values from the outmost surface of composite Al layer to the magnesium alloy substrate. Results of electrochemical corrosion test of the composite plate in 5 wt.% NaCl solution showed the better protection effect of the composite Al layer on the magnesium alloy in a corrosion medium. Almost the same corrosion level on the whole corrosion surface was observed which indicated the highly uniform microstructure of the composite layer. It was also proved that the plain arches on the outmost surface of the composite Al layer had no influence on the corrosion resistance of composite Al layer.

Influence of Friction Stir Welding Process on the Weld Formation and Tensile Strength of Titanium and Aluminum Dissimilar Alloys Welded Joint

Titanium alloy TC1 and Aluminum alloy LF6 were jointed by friction stir welding (FSW), and the influence of process parameters on formation of weld surface, cross-section morphology and tensile strength were studied. The results show that, Titanium and Aluminum dissimilar alloy is difficult to be joined by FSW, and some defects such as cracks and grooves are easy to occur. When the rotational speed of stir head(n) is 750r/min and 950r/min, the welding speed(v) is 118mm/min or 150mm/min, a good formation of weld surface can be obtained, but the bonding of titanium/aluminum interface in the cross-section of weld joint is bad when n is 750r/min which results in a low strength joint. When n is 950r/min and v is 118mm/min，the strength of the FSW joint of Titanium/Aluminum dissimilar materials is 131MPa which is the highest．

Study on the Resistance Spot Microwelding Parameters of Copper and Nickel-Plated Steel Dissimilar Metals

0.2-mm-thick copper and 0.3-mm-thick nickel-plated steel dissimilar metals were jointed by resistance spot microwelding. The processing parameters were optimized by orthogonal experimental and influence of processing parameter on the morphology and microstructure of welded joint was studied. The results show that the optimized processing parameters that can get the maximum tensile-shear force are: preheat current is 0.8KA, welding current is 3.5 KA, up time is 0.5ms, preheat current is 2ms, cool time is 0.5ms, welding time is 5ms, and electrode pressure is 20N. With the optimized processing parameters, the tensile-shear force of the welded joint can achieve 108.9N. The microstructures of welded joint that has best tensile-shear force are composed of swirling structure in weld nugget, uniform distribution of copper in weld nugget with a little of nickel.

Effect of Bonding Temperature on Microstructure Development during Transient Liquid Phase Bonding of Ti 2 AlNb Alloy Using Ti-Zr-Cu Based Filler Alloy

Transient liquid phase (TLP) bonding of Ti2AlNb, used for vacuum brazing furnace, was carried out using Ti-Cu-Zr based foil as filler alloy at 950, 1000 and 1050°C. The effect of bonding temperature on joint interface, phase constitutions and their distributions were investigated by taking advantages of OM, SEM, EDS and XRD analyses. The result revealed that the TLP joint consisted of isothermally solidified zone and diffusion affected zone. A non-isothermally solidified zone existed only when the bonding temperature was not high enough. The interface morphologies of the joints were found to be very sensitive to the bonding temperature. With the bonding temperature increased from 950°C to 1000°C, the width of non-isothermally solidified zone decreased from 69 μm to 23 μm. When the bonding temperature was 1050°C, the non-isothermally solidified zone disappeared. Meanwhile, more alloying elements of Cu and Zr diffused most adequately into the base material. Phase analysis showed that along with the increasing of bonding temperature, the secondary phase constitution of joint changed from Ti (Cu,Al)2 + AlNb2 + Ti solid solution to Ti solid solution + Nb (CuAl) + Al4Cu9 + Al2Zr3, and the proportion of secondary phase was 35.7%, 20.2%, 6.7%, respectively. The morphology of base metal changed because of the relatively high bonding temperature was higher than 980°C, the α→β transition temperature.

Preparation and Mechanical Property of MWNTs/Al Composite Wires by Rotational Friction Extrusion Processing

The multi-walled carbon nanotubes (MWNTs) reinforced aluminum composite wires were fabricated by Rotational Friction Extrusion Processing (RFEP). The microstructure and mechanical properties of MWNTs/Al composite wires with different content of MWNTs were investigated. The results show that carbon nanotubes were well dispersed into the aluminum matrix, and the mechanical properties of MWNTs/Al composit wires were improved by FSP and RFEP. The tensile strength reached up to 186.3MPa when 4.5vol% MWNTs was added, which was 1.13 times that of MWNTs/Al composite blocks prepared by FSP only.

The Rotational Extrusion Alloying

The Rotating Extrusion Alloying (REA) is a process which combined friction stir welding process and extrusion technology. In the REA process, dissimilar metals are mixed, cracked, and subjected to high speed, severe pressing deformation, and therefore rapidly alloy at a low temperature. The result shows that REA technology can be alloyed Al-Ti material. Its phases are mainly composed of Al and Al3Ti, which are distributed more evenly in the aluminum. After heat treatment, its phases’ types and pole figures have no significant change, but there is a trend of transition to the non-equilibrium stable phase. Small-angle grain boundaries decrease or even disappear.

Study on the Microstructure and Properties of Zl114a Friction Stir Welded Joint with Forced Cooling

ZL114A was joined by friction stir welding and liquid nitrogen was used to cool the welded joint during the welding process. The Influence of forced cooling on the microstructure and properties of welded jointed was studied. The results show that, when forced cooling is used, the amount of silicon particles in weld nugget zone is larger and the size is more homogeneous, the size of silicon particle in heat-mechanical affected zone is more fine , the grain size of heat affected zone is half of air cooling welded joint and the amount of Al-Si eutectic is smaller than air cooling welded joint. The micro hardness increases after forced cooling is used, the hardness of weld nugget zone is 20Hv higher than air cooling welded joint. The strength of forced cooling welded joint increases 13.6% than air cooling welded joint.