Key Engineering Materials Vol. 693

Abstract: CAD/CAM technology has been widely applied in the field of oral restoration, which creates a revolutionary change in the pattern of traditional handmade denture and puts forward new demands on the past medical dental restorative material. The materials used for making dentures should own good machining properties and biocompatibilities. Medical zirconium ceramic have a broad prospect in the field of oral restoration because of its features are high strength, high toughness, good biocompatibility, high similarity of performance and aesthetic effect of processed dentures to real dentals. Dental restoration was obtained initially by NC machining using the feature that zirconium ceramic was not fully hardened but had a definite range of strength in the semi-sintered state. Experimental results shown that the ceramic denture machined by this processing has better surface quality and can satisfy requirements of oral restoration. Observation results shown that cutting surfaces were smooth, grinding cracks were tiny and uniform, and there were no obvious fracture gaps on edges and complex irregular surface of neck could be better reflected.

Abstract: In this paper, the coating was prepared by the slurry pack cementation on the surface of Fe-14Mn-6Si-5Ni alloy at 900°C for 10 h. A slurry pack cementation mixture was composed of Cr₂O₃ used as chrominizing source, pure Al powder as reducer, an activator of NH₄Cl and albumen (egg white) as cohesive agent. The microstructure, wear resistance and corrosion resistance of coating has been studied. The results showed that the microstructure of the coating is composed of solid solution with Al and Cr; the microhardness of coating with a value of 460 HV was 1.4 time than that of the matrix alloy, friction coefficient of the coating was 0.35, 1/2 of that of matrix alloy, and the rate of corrosion of coating was lower one order of magnitude than that of the FeMnSi based alloy.

Abstract: Microscopic observation and testing were carried out on the structure & texture, bonding form and performances of different plasma-sprayed ceramic coatings on the wear surface of Cr12MoV dies by KYKY-2800B SEM. The result indicates that the bonding between the coating and the die matrix surface is mainly of mechanical form, the bonding strength of coating is higher than that of the matrix material, the coating has a low structural porosity and the hardness and friction performance of the die surface are somewhat improved. Compared with the original dies, not only their dimensional accuracy and quality standard are no lower but also their performance such as wear resistance and corrosion resistance are better, fully satisfying the requirements of die repair & remanufacture.

Abstract: SiC₂ nanoparticles to aluminum alloy surface performance by the friction stir processing (FSP) was studied in this paper, the results showed that the SiC₂ nanoparticles to aluminum alloy surface performance by the FSP can improve the microhardness of the aluminum alloy surface, which further showed that by the method of modification aluminum alloy surface had the resistance performances of the wear and corrosion. At the same time, by the sample microstructure pictures can see, when the tool rotation speed was 1000 r/min and the welding speed was 110 mm/min, the obtained grains were tiny and the distribution of SiC₂ nanoparticles was the most uniform. When the tool rotation speed was 1000 r/min and the welding speed was 110 mm/min, the obtained grains were coarse and the distribution of SiC₂ nanoparticles was the most uneven. This showed that in FSP the main factor of generated higher friction heat was the tool of rotational speed, this was the main factors to ensure grain happen recrystallization. The fastest dissipation heat of the factor was the welding speed, this was the main factor of fine grain.

Abstract: By conducting the quasi-static compression and split Hopkinson pressure bar testing,the flow strain - stress curves under strain rate range of 0.0001-1000/s and temperature range of normal-400°C of different volume fraction SiC particles reinforced metal matrix composite SiCp/6063Al were obtained. The commonly used Johnson-Cook constitutive model in metal materials was applied in this research. And on the basis of it, the influence of volume fraction to flow stress was utilized to establish the equivalent and homogeneous constitutive model.

Abstract: The orthogonal experimental study is carried out to study the Incorporation of different proportion of functional components and the effect on tribological performance among semi-metallic friction materials. A test is conducted for each sample on XXD-MSM constant speed tester in accordance with Brake Linings for Automobiles (GB5763-2008). The friction factor and high-temperature abrasion resistance properties are evaluated along with the obtaining of optimal formula, and the mechanism of affecting the tribological properties is analyzed on the worn surfaces by using a scanning electron microscope (SEM). The study results indicate that the high-temperature friction stability could be deeply affected by the adequate content of steel fiber, Kevlar pulp, potassium hexatitanate whisker and cashew nut shell. The mechanism of High-temperature tribological behaviors are the thermal decompositions. The thermal decomposition of organic matter might greatly weakened the bonding effect. The thermal decomposition of tribo-film fall off as lamellar chip under the effect of friction stress. The addition level of nanoparticles is 3%, the sample’s tensile strength, tensile strength, hardness index and noise level are better. If the modified resin is further applied, this formula can be close to the index of excellent Chinese industrial product JF04-20.

Abstract: A novel starch-g-poly (acrylic acid) hydrogel was prepared by graft-copolymerization among starch, acrylic acid in aqueous solution with potassium persulfate as an initiator, N, N-methylenebisacrylamide as a crosslinking agent. Characterization of the graft copolymer was carried out by X-ray diffraction, FTIR and SEM analytical methods. Swelling kinetic analysis in distilled water was done to study the swelling behavior of the product. The results show that the product exhibits water absorption of 786g/g in distilled water at ambient temperature. It has been proved that the grafting of acrylic acid onto starch was successful and the aggregation of phase of native starch was changed from semi-crystalline state to amorphous aggregation state due to copolymerization.

Abstract: Microstructure properties of PbO-TiO2-SiO2 system sealing solder for vacuum glazing was studied. Sealing solder was placed on the sealing glass substrate. Samples were obtained by sintering at different temperatures. The microstructure properties and binding properties with soda lime glass substrate at different temperatures was observed and studied. Micro hardness of the sealing solder after sintering were tested. The results show that in the solder sealing temperature, a transition layer was formed gradually between the sealing solder and the glass substrate as the sintering temperature increases. PbO and SiO2are main ingredients of the transition layer. This layer performed tight connection with the glass substrate after it was completely formed. The interface between sealing solder and soda lime glass substrate showed good performance. PbO-TiO2-SiO2-RxOy system is an ideal sealing material for the production of vacuum glazing.

Abstract: This paper makes PF weaving friction material (p0.0) from tung oil, PF weaving friction material (BP) from boric acid, modified PF weaving friction material (SP) of nanopalygorskite by in-situ method, and modified PF weaving friction material (MP) of nanopalygorskite by blending method. The contrast tests of frictional properties are carried out on DMS-1 friction-abrasion tester. Hot recession test is performed on CHASE-M600 testing machine, and surface appearance analysis of friction sample is made on electronic probe. The result shows that after modification, the heat resistance and thermal stability of PF are all improved to different extent. SP friction material has best thermal stability and strongest braking ability under high temperature; while BP takes second place, and P0.0 is the worst. The heat resistance of BP, SP and MP is stronger than P0.0. The critical temperature of hot recession for weaving friction material on the base of nanopalygorskite/tung oil PF raises by 40~50°C. On the aspect of frictional properties, friction coefficients of SP, BP, and MP show quite stable. Among these samples, SP has the most stable friction coefficient, and P0.0 the worst. The wear rate of SP, BP and MP has the same trend with the temperature changes. However, the wear rate of P0.0 is getting intense with temperature rise. Its wear rate is much higher than SP, BP, and MP’s under same temperature.

Abstract: A nanoporous copper (NPC) sample with well-ordered porosity of 20 nm was fabricated by an electrochemical dealloying single-phase Cu0.4Mn0.6 with an external potential of-0.5 V (MSE). The electrochemical mechanism of the dealloying process on the Cu-Mn surface was studied by a liner sweep voltammetry experiment, and an optimized applied voltage for the Cu-Mn system was recommended. The properties of the monolithic NPC, including morphology, chemical composition, surface area and wettability were systematically characterized. The specific surface area around 11.86 m2/g of the as-dealloyed NPC was measured by BET-nitrogen method. The micro/nanoscale bi-continuous 3D porous structures of NPC not only increase the surface area, but also improve the wettability of NPC surface since the increase in surface roughness.