The high interfacial thermal resistance, poor dispersion, and insufficient contact of the fillers in polymer-based composites result in a lower thermal conductivity, restricting the development of heat conduction and dissipation industrial application. In this paper, bioinspired modification of poly(dopamine) (PDA) was applied to improve the interfacial adhesion performance of copper nanospheres (Cu) and carbon nanotubes (CNTs) in a poly(vinylidene fluoride) (PVDF) matrix. The synergistic effect of Cu and CNTs with different dimensions was beneficial to the formation of a continuous heat conduction network. Moreover, CNTs could reduce the distance that linked the adjacent Cu with the PVDF matrix and fill the defect vacancies. The PVDF composite with 30 wt % Cu and 5 wt % CNT achieved a high thermal conductivity of 1.44 W/(m·K) and a tensile strength of 95 MPa. The simulation analysis of the model indicated that the interconnected architecture of the CNT/Cu/PVDF/PDA composite reduced the interfacial thermal resistance by the bridging effect of CNTs. The long-term heat-transfer test with the corrosive medium showed that a high-performance polymer heat exchanger will have great application potential in the field of waste heat recovering.
Pure titanium (Ti) which had been processed by high energy ball milling, graphite and Ni60A self-melting alloy composite powder were used as the cladding materials. A test on the in situ synthesized graded TiC particulate reinforced Ni-based composite coating was carried out after presetting of the composite powder on the 42CrMo alloy structured steel base surface. Morphologies, tissue structures and microhardness values of samples were investigated by an optical microscope (OM), scanning electron microscope (SEM) and microhardness tester. Results show that in situ synthesis of TiC reinforced particulates is realized with pure Ti and graphite powder under laser cladding. TiC particulates which have a small density presents a graded distribution of less at lower and more at upper of the coating due to the floating effect in a melting pool. Therefore, in situ synthesized graded TiC particulate reinforced Ni-based composite coating was gained. Moreover, TiC particulates cluster and grow in the melting pool due to collision and bonding of TiC particulates in the floating process. Compared to TiC particulates at lower part of the coating, the TiC particulates at upper part of the coating possess a higher proportion of clusters and growth phenomena. The volume percentage of TiC particulates at middle and bottom of the composite coating is lower than 5%, while volume percentage of TiC particulates on the coating surface is no higher than 25%. Similar with distribution pattern of TiC particulates, microhardness of the composite coating is also high on surface and low deep layer of the coating.
In order to choose the rubber material and improve the service life of Progressing Cavity Pump (PCP ) when exploiting offshore crude oil, it is important to analyze friction and wear behaviour of stator and rotor of PCP in the mixture of crude oil with different water content. The friction and wear test about Nitrile -Butadiene Rubber (NBR) and Fluorine Rubber (FKM) were carried on ring-on-block tester, the wear loss was observed by electron microscope, the wear mechanism was also discussed. The results show that: (1) FKM owns better wearing resistance than NBR in the mixture of crude oil with different water content; (2) when the content of water in the mixture is less than 26%, the frictional coefficient of sample is 0.05, due to the oil film between the friction pairs; (3) when the content of water in the mixture is more than 26%, the frictional coefficient increases to 0.4, because of the water film between the friction pairs.
Ni-Al2O3 nano-composite coating was prepared on the ASP30 powder metallurgical steel surface for semiconductor encapsulation mould by using electrodeposition method. Effects of Al2O3 contents on microstructure, microhardness and wear resistance of composite coating were analyzed. Results demonstrate that due to refined crystalline strengthening, dispersion strengthening and high-density dislocation strengthening of Al2O3 nanoparticles in uniform distribution, Ni-Al2O3 nano-composite coating has more compact structure and smaller grain size compared to the pure Ni coating, which are conducive to increase microhardness and wear resistance of the coating significantly. Neither too low nor too high Al2O3 contents is beneficial to improve microhardness and wear resistance of composite coating. The pure Ni coating has serious adhesion wearing, while the nano-composite coating with the moderate Al2O3 content has the best performance and it mainly has mild abrasive wear, accompanied with some adhesion wearing. Relatively serious adhesion wearing occurs on the wear surface of pure Ni coating. Differently, wearing surface of Ni-Al2O3 nano-composite coating is mainly dominated by mild abrasive wear, accompanied with some adhesion wearing. Neither too low and too high Al2O3 content is conducive to improve microhardness and wear resistance of composite coating.
In order to reduce the thermal stress at clad layer and further reduce the crack generation in the laser cladding process, a method of controlling the cracks at clad layer by changing the laser energy density was proposed. The comparative thermal-mechanical coupling nite element analysis was conducted for the uniform rectangular spot and convex shape beam spot cladding processes on plasma-sprayed MCrAlY coating through the numerical simulation method based on the ANSYS software. The results show that the rapid heating and cooling characteristics, which are typical in laser processing, are manifested in the cladding process using the uniform rectangular spot, and the convex shape spot can exert the preheating and slow cooling effects to a certain extent, so as to reduce the temperature gradient of the cladding zone and non-cladding zone. In addition, on the precondition of equivalent cladding effect, the thermal stress at the clad layer is also low, so the cracking tendency of the clad layer can be effectively mitigated. Relative to the laser beam shaped diffractive optical element special for design and manufacturing, superposing two uniform rectangular spots with different sizes and energy densities is a simpler and more effective method of acquiring the convex shape spot.
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