G.Montay
,
A.Cherouat
,
A.Nussair
,
J.Lu
材料科学技术（英文）
Residual stress in coatings is the result of individual particle stress. Their effects may be either beneficial or detrimental, depending upon the magnitude, sign and distribution of the stresses with respect to the external load. Tensile stress which exceeds the elastic limit causes cracking in surface coatings or at the interface between the substrate and the coat. Compressive stress, in general, has a beneficial effect on the fatigue life, crack propagation, coating adhesion and on the durability of the top coat during service. Compressive residual stresses can increase the number of cycles before crack initiation begins through a mean stress effect. Temperature gradients which occur during solidification and subsequent cooling are the principal mode of internal stresses generation. Some parameters influence the residual stress field of both the coating and the substrate. Substrate nature, spraying temperature, thickness of the coat layer, substrate preparation (grit blasting conditions), and velocity of the splats are in the relation with the quality of the coating. In this work, we will describe the role playing by the ceramics coating elaboration on the residual stress gradient in depth of the component. The incremental hole drilling technique has been developed to determine the residual stress gradient in depth of the coat and substrate which must be used with particularly conditions. This new technology has been employed on zirconia, alumina and tungsten carbide plasma sprayed coating.
关键词:
Coating
,
null
,
null
,
null
Xiancheng ZHANG
,
Jianming GONG
,
Sh
,
ong TU
材料科学技术（英文）
The thermomechanical behavior and the distribution of residual stresses due to thermal spraying of NiCoCrAlY coating were studied by thermomechanical finite element analysis. The effects of phase transformation due to solidifying process of coating particles, thickness and material properties of coating on the residual stresses were discussed. Results showed that residual stress decreases little with the stress relaxation due to the phase transformation. For the substrates with the same thickness, the residual stress increases with the increase in coating thickness. The state of
residual stresses relates to the material properties of coating and substrate closely. The stress-induced failure model of coating is also discussed.
关键词:
Coating
,
null
,
null
,
null
Wan Peng
,
Tan Lili
,
Yang Ke
材料科学技术（英文）
doi:10.1016/j.jmst.2016.05.003
Magnesium (Mg) and its alloys as a novel kind of biodegradable material have attracted much fundamental research and valuable exploration to develop its clinical application. Mg alloys degrade too fast at the early stage after implantation, thus commonly leading to some problems such as osteolysis, early fast mechanical loss, hydric bubble aggregation, gap formation between the implants and the tissue. Surface modification is one of the effective methods to control the degradation property of Mg alloys to adapt to the need of organism. Some coatings with bioactive elements have been developed, especially for the micro-arc oxidation coating, which has high adhesion strength and can be added with Ca, P, and Sr elements. Chemical deposition coating including bio-mimetic deposition coating, electro-deposition coating and chemical conversion coating can provide good anticorrosion property as well as better bioactivity with higher Ca and P content in the coating. From the biodegradation study, it can be seen that surface coating protected the Mg alloys at the early stage providing the Mg alloy substrate with lower degradation rate. The biocompatibility study showed that the surface modification could provide the cell and tissue stable and weak alkaline surface micro-environment adapting to the cell adhesion and tissue growth. The surface modification also decreased the mechanical loss at the early stage adapting to the load-bearing requirement at this stage. From the interface strength between Mg alloys implants and the surrounding tissue study, it can be seen that the surface modification improved the bio-adhesion of Mg alloys with the surrounding tissue, which is believed to be contributed to the tissue adaptability of the surface modification. Therefore, the surface modification adapts the biodegradable magnesium alloys to the need of biodegradation, biocompatibility and mechanical loss property. For the different clinical application, different surface modification methods can be provided to adapt to the clinical requirements for the Mg alloy implants.
关键词:
Bio-adaptability
,
Coating
,
Biodegradable
,
Magnesium alloys
,
Orthopedic implants
Minh-quy Le
,
Young-hun Chae
,
Seock-sam Kim
材料科学技术（英文）
The sliding wear behaviors of a single layer Al2O3-30 wt pct ZrO2, a double layer Al2O3-30 wt pct ZrO2/Ni-Cr and a single layer Al2O3-13 wt pct TiO2 coating deposited on low carbon steel by plasma spraying were investigated under lubricated conditions with various normal loads. The plastic deformation, detachment and pull out of splats were involved in the wear process of the studied coatings under test conditions. Crack propagation was found in Al2O3-13 wt pct TiO2 under loads of 70 and 100 N and in Al2O3-30 wt pct ZrO2/Ni-Cr under a load of 130 N. While increasing the normal load, the wear rates of Al2O3-30 wt pct ZrO2 and Al2O3-30 wt pct ZrO2/Ni-Cr slightly increased, the wear rate of Al2O3-13 wt pct TiO2 increased rapidly. The results showed that the Ni-Cr bonding layer improved the wear resistance of the coating system even it is relatively thin compared with the outer coating layer. The influence of this bonding layer on wear behavior of the coating increased as increasing the normal load.
关键词:
Coating
,
null
,
null
H.Zhang
,
G.Wei
,
L.Zheng
,
L.Li
,
X.Y.Wang
,
A.Vaidya
材料科学技术（英文）
A good understanding of melting and resolidification of the substrate will help us to achieve better bonding. A numerical model is developed to investigate the solidification of the droplet, and melting and resolidification of the substrate. The molybdenum powder spraying onto three different substrates: a stainless steel, brass (70%Cu) and aluminum by atmospheric plasma spraying has been investigated. The maximum melting depth of the substrate has been measured and compared with the numerical prediction. Experimental results show that the material properties of the splat and substrate and melting temperature of the substrate play the important roles on substrate melting. A dimensionless parameter, temperature factor, has been proposed and served as an indicator for substrate melting.
关键词:
Thermal spraying
,
null
,
null
,
null
,
null
Yanjin LU
,
Lili TAN
,
Hongliang XIANG
,
Bingchun ZHANG
,
Ke YANG
金属学报(英文版)
A composite coating was fabricated on pure magnesium by hydrothermal treatment in order to reduce its degradation in body environment. The coating was characterized by scanning electron microscopy (SEM) and X-ray diffraction (XRD). The XRD pattern showed that the main composition of the coating was a mixture of CaSiO3, MgSiO3 and Mg(OH)2. Electrochemical test showed that the corrosion current density (emcorr) of the coated magnesium was decreased by about two orders of magnitude compared with that of the bare magnesium, and the EIS measurement also showed that the corrosion resistant performance of the coated magnesium was significantly enhanced. Meanwhile, weight loss test showed that the weight loss of the coated magnesium was lower than that of the bare magnesium. Hence, the present study indicated that the composite coating could greatly slow down the degradation of pure magnesium.
关键词:
Magnesium
,
null
,
null
,
null
,
null
Jihui WANG
材料科学技术（英文）
MoS2 coatings were prepared using an unbalanced bipolar pulsed DC (direct current) magnetron sputtering apparatus under different targets, cathode current densities, power modes and bias voltages. The morphology, structure and growth characteristics of MoS2 coatings were observed and identified respectively by scanning electron microscopy, X-ray diffractometry and mass spectrometry. The results show that MoS2 coatings evolve with the (002) basal plane parallel to the surface by using cold pressed target with lower density, lower cathodic current density, bipolar pulse DC power and minus bias voltage, whereas the coatings deposited under hot pressed target, higher cathodic current density, simple DC power and positive bias voltage have the (002) basal plane perpendicular to the surface. The influence of deposition conditions on the crystal structure of MoS2 coating is implemented by altering its growth rate and the energy of sputtering-deposition particles.
关键词:
Deposition condition
,
null
,
null
,
null
Z.G.Liu
,
B.Gabbitas
,
D.L.Zhang
,
J.Liang
,
W.Gao
材料科学技术（英文）
The production and microstructural characterization of two types of ceramic particulate reinforced Ti matrix composites (TMCs): Ti-6Al-4V/10~vol. pct TiB and Ti(Al,O)/58 vol. pct Al2O3 were studied. The Ti-6Al-4V/10 vol. pct TiB composite with refined microstructure has been produced using a combination of high energy mechanical milling and hot isostatic pressing. The Ti(Al,O)/58 vol. pct Al2O3 in-situ composite powder has been produced using a novel powder processing process which involves high energy mechanical milling of a mixture of Al and TiO2 powders to produce an Al/TiO2 composite powder followed by thermal treatment of the composite powder. The Ti(Al,O)/58 vol. pct Al2O3 composite powder has been used to produce coatings. Selected mechanical properties of the Ti-6Al-4V/10 vol. pct TiB composite and the high temperature oxidation resistance have also been evaluated.
关键词:
Ti alloy
,
null
,
null
,
null
Xinwen ZHU
,
Dongliang JIANG
,
Shouhong TAN
材料科学技术（英文）
An innovative approach has been developed to fabricate reticulated porous ceramics (RPCs) with uniform macrostructure by using the polymeric sponge as the templates. In this approach, the coating process comprises of two stages. In the first stage, the thicker slurry was used to coat uniformly the sponge substrate. The green body was preheated to produce a reticulated perform with enough handling strength after the sponge was burned out. In the second stage, the thinner slurry was used to coat uniformly the preform. The population of the microscopic and macroscopic flaws in the structure is reduced significantly by recoating process. A few filled cells and cell faces occur in the fabrication and the struts were thickened. A statistical evaluation by means of Weibull statistics was carried out on the bend strength data of RPCs, which were prepared by the traditional approach and innovative approach, respectively. The result shows that the mechanical reliability of RPCs is improved by the innovative approach. This innovative approach is very simple and controlled easily, and will open up new technological applications for RPCs.
关键词:
Reticulated porous ceramics
,
null
,
null
,
null
,
null
Fei CAI
,
Chungen ZHOU
,
Huibin XU
,
Shengkai GONG
材料科学技术（英文）
An oxidation resistant Al-Cu-Fe quasicrystalline coating was fabricated on substrate of Ti alloy by low pressure plasma spraying (LPPS) method. As-sprayed Al-Cu-Fe coating has a rapidly solidified lamellar microstructure consisting of quasicrystalline phase and crystalline phase. The formation of quasicrystalline coating is related to the annealing. The results from the oxidation experiments showed that Al-Cu-Fe quasicrystalline coating improved the oxidation resistance of Ti-base alloys. During the oxidation period there is no evident spallation of the coating from the substrate. Oxide formed on the surface of Al-Cu-Fe quasicrystalline coating after oxidation consisted of Al¬2O¬3. Oxidation occurs leading to a change of concentration and phase transformation in the coating surface. Selective oxidation of Al transforms the quasicrystalline phase into the phase.
关键词:
Low pressure plasma spray
,
null
,
null
,
null
,
null
