Jianhong Wang

Processing and Characterization of Core-Shell PA12/Silica Composites Produced by Selective Laser Sintering

Silica particles coated with PA12 by emulsion polymerization were used as fillers to reinforce PA12 based composites prepared by selective laser sintering (SLS). The influences of the treated and untreated particles on the sintering behavior and mechanical properties of the laser sintered specimens were investigated. It was found that there were many uneven holes in the untreated composites. However, for the treated composites, due to the silica particle surfaces treated by emulsion polymerization, the absorbance of laser was improved and the particles dispersed well in the polymer matrix; a full dense structure was obtained and the properties were enhanced, such as the tend strength increased 30%, the maximum value was 34MPa; the tensile strength increased up to 125%, the maximum value was 44.2 MPa, comparing to the unfilled PA12. Drawing from the results, it can be confirmed that a full dense structure can be obtained and the PA12 matrix was strengthened and toughened when the silica particles were coated with PA12 by emulsion polymerization.

Experimental and theoretical insight into the cooperativity effect in composite wax powder and ternary complex of coronene with CH4 and Mn+ (Mn+ = Li+, Na+, K+, Be2+, Mg2+ or Ca2+)

ABSTRACT The experimental infrared (IR) spectrum of composite wax powder was investigated. The frequency shifts of the C=C anti-symmetrical stretching mode were observed and the experimental cooperativity effect involving Na+···π interaction was suggested. In order to further reveal the nature of cooperativity effect, the interaction energies in Mn+···coronene···CH4 (Mn+ = Li+, Na+, K+, Be2+, Mg2+ or Ca2+) as the model systems of composite wax powder were calculated by using the B3LYP, M06-2X and MP2 methods with 6-311++G** basis set. The results show that the Mn+···π interactions were strengthened upon the formation of ternary complexes. Although the changes of absolute values of the interactions between CH4 and coronene were not obvious, the relative values were considerably significant upon the formation of ternary complexes. The cooperativity effect was perhaps the reason for the formation of notable advantage of composite wax powder upon the introduction of surfactant with cation into wax powder. Reduced density gradient and atoms-in-molecules analysis confirm the cooperativity effect in Mn+···coronene···CH4, and reveal the nature of the formation of the predominant advantage of composite wax powder.

Temperature Distribution Laws During Selective Laser Melting Process of Nickel Base Alloy GH4169

In this paper, the temperature distribution laws during selective laser melting process of GH4169 alloy were studied. When the laser power was certain, with the scanning speed reduced the temperature of the melt pool increased, which caused the accumulation of lot of heat, and making the maximum temperature over the boiling point of metal, and thus resulted in the melt pool splash and hence affected the quality of forming. When the scanning speed was a constant, with the increase of laser power, the maximum temperature in melt pool increased. And when the laser power was more than 300 W, it was prone to give rise to the vaporization of powder, and reduced the forming quality. During the forming process, the spot center temperature of each scan line decreased firstly and then increased. The temperature increased in the head and the tail of the scan line, and was stable in the middle of the scan line. The change of midpoint temperature of the scan line was stable, which ensured the performance of each layer was consistent during multi-layer scan process.

Laser Cladding of Titanium Alloys with Ti+Al+C Powders

Laser surface cladding of Ti6Al4V alloy by Ti+Al+C powders (Titanium and carbon powders with an atomic ratio of 1:1 were mixed with 20-60wt.% aluminum powders) was investigated using CO2 laser. TiC particles were in situ formed mainly during the solidification and sizes of TiC particles were varied according to different contents of aluminum powders in the Ti+Al+C system. The results show that the coating had good metallurgical bonding with substrate when Al content was 20% or 40%. The microhardness of coating is 738HV0.5 which was 2 times as that of the Ti6Al4V alloy approximately. The wear resistance of TiC/Al ceramic layer was approximately 3 times greater than that of the Ti6Al4V substrate. 1

Effect of Al Content on the Microstructure and Property of TiC/Al Ceramic Matrix Coating Deposited by Laser Cladding on Ti-6Al-4V Alloy

Laser surface cladding of Ti-6Al-4V alloy by Ti+C+Al powders (Titanium and carbon powders with an atomic ratio of 1:1 were mixed with 20-40wt.% aluminum powders) was investigated. TiC particles were in situ formed mainly during the solidification. Effect of Al content on the porosity and microstructure of the cladding layer was studied. The resultant microstructure in the modified surface layer was characterized and the micro-hardness on the cladding layers was measured, as well as the wear rates. The results show that the coating had good metallurgical bonding with substrate when the Al mass fraction in Al-Ti-C system is 30 %. The micro-hardness of coating is 802HV0.5 which is 2~3 times as that of the Ti-6Al-4V alloy approximately.