Study on the subsonic speed flame spraying coating of hydroxyapatite

A new method of preparation of biomaterial composite coating by the technique of subsonic thermal spraying was discussed in this paper. Ti6Al4V and pure Ti were chosen as substrate and sublayer material respectively and the working layer was sprayed with biomaterial hydroxyapatite (HAP), forming the composite coating. The experiments of heat shock and tensile strength showed that the bonding strength between coating and substrate is almost as same as that of specimen in which Ni/Al powder was adopted as sublayer. The phases of TiN, TiO2, and Ti2O3 were formed in the sublayer, which are free of toxic and have no side effects. The powder of working layer HAP was decomposed partly during spraying, but it can be solved by later treatment.     

Application of the Same-Stuff and Equal-Strength Laser Cladding Technology on the Repaired Semishrouded Impeller

0Cr17Ni4Cu4Nb powder was used to investigate the same-stuff laser repair(LR)technology on the semishrounded impeller.To improve the repaired effect,heat treatment was used after LR forming process.By means of optical microscopy,scan electron microscopy(SEM),micro-hardness tester and tensile tests,the microstructure of the coating was investigated and mechanical properties were measured.The experimental results show that cladding layer is well bonded to the substrate,the microstructure of the laser repaired zone(LRZ)is coarse martensite which will be refined after heat-treatment.The mechanical property experiments indicate that the micro-hardness and toughness would be increased after heat-treatment,the strength of LRZ after heat-treatment is 1050～1200 MPa,while the strength of normal laser repaired sample is 1000～1050 MPa.The refinement effect due to the heat treatment plays an important role in the improvement of the mechanical properties of samples.Overspeed examination and the real operation of the impeller after repairing also confirmed the reliability of this same-stuff and equal-strength laser cladding technology.     

Surface Characteristics and Indentation Deformation of Porous Anodic TiO2 Layer Before and After Hot Water Treatment

Hot water treatment was performed to modify the surface of porous TiO2 layer prepared by anodic spark oxidation technique for better biocompatibility.The oxide layer without water treatment exhibited a porous surface with few nanometer features and consisted of poorly crystallized oxides.During water treatment,the poorly crystallized oxides were transformed into crystalline anatase gradually and numerous nanoparticles formed on the oxide surface,leading to increased surface roughness at the nanoscale.The indentation deformation behaviors of oxide layer before and after water treatment were investigated and compared.Results show that under the indentation load,the untreated anodic TiO2 layer exhibited good adhesion to the substrate.In contrast,after water treatment,apparent oxides pile-up and spallation were observed around the indentation,indicating decreased adhesion strength.     

Microstructure and mechanical properties of Al-B_4C composite at elevated temperature strengthened with in situ Al_2O_3 network

This study evaluated the mechanical properties and thermal properties of Al-12 vol%B_4 C composite at elevated temperature strengthened with in situ Al_2 O_3 network.The composite was fabricated using powder metallurgy(PM) with raw materials of fine atomized aluminum powders,and the associated microstructures were observed.At 350 ℃,the composite had ultimate tensile strength of UTS=137 MPa,yield strength of YS_(0.2)=118 MPa,and elongation of ε=4%.Besides,the mechanical properties of the composite remained unchanged at 350℃ after the long holding periods up to 1000 h.The excellent mechanical properties and thermal stability at 350℃ were secured by in situ am-Al_2 O_3 network that strengthened the grain boundaries.The interfacial debonding and brittle cracking of B_4 C particles were the main fracture mechanisms of the composite.In addition,the influence of sintering temperature and rolling deformation on the microstructures and mechanical properties was studied.     

Microstructure and mechanical properties of Mg-6A1-4RE-0.4Mn alloy

Mg-6Al--4RE-0.4Mn （mass fraction, %, RE=Ce rich mischmetal） alloy was prepared by steel mould casting technique. Solid solution and artificial aging （T6） were carried out. The microstructure and mechanical properties of both as-cast and T6 treated alloys were investigated at room temperature and 423 K. It is found that the intermetallic compounds of the as-cast and T6 treated alloys were mainly composed of Al11RE3, Mg17Al12 and Al6REMn6. The Vickers hardness （Hv） of the as-cast alloy is 63 and it increases to 70 after T6 heat treatment. T6 heat treatment plays a slight role in the tensile properties at room temperature, but the yield strength and elongation of T6 state at 423 K are distinctly improved. The yield strength and elongation of the as-cast alloy at 423 K are 71 MPa and 18%, respectively, and the values increase after T6 heat treatment, which is attributed to Al11RE3, Mg17Al12 and Al6REMn6 precipitates that impede the dislocation movement and gliding of grain boundaries effectively.     

Effect of hot extrusion process on microstructure and mechanical properties of hypereutectic Al-Si alloys

The hypereutectic Al-Si alloy was fabricated by hot extrusion process after solidified under electromagnetic stirring,and the microstructure and mechanical properties of the alloy were studied.The results show that the ultimate tensile strength and elongation of the alloy reached 229.5 MPa and 4.6%,respectively with the extrusion ratio of 10,and 263.2 MPa and 5.4%,respectively with extrusion ratio of 20.This indicates that the mechanical properties of the alloy are obviously improved with the increase of extrusion ratio.After hot extruded,the primary Si,eutectic Si,Mg2Si,AlNi,Al7Cu4Ni and Al-Si-Mn-Fe-Cr-Mo phases are refined to different extent,and the efficiency of refinement is obvious more and more with the increase of extrusion ratio.After T6 heat treatment,the sharp corners of these phases become passivated and roundish,and the mechanical properties are improved.The ultimate tensile strength of the extruded alloy after T6 heat treatment reaches 335.3 MPa with extrusion ratio of 10 and 353.6 MPa with extrusion ratio of 20.     

Influence of hot extrusion on microstructure and mechanical properties ofAZ31 magnesium alloy

Extrusion treatment is a common method to refine the grain size and improve the mechanical properties of metal material. The influence of hot extrusion on microstructure and mechanical properties of AZ31 magnesium alloy was investigated. The results ,show that the mechanical properties of AZ31 alloy are obviously improved by extrusion treatment. The ultimate tensile strength （UTS） of AZ31 alloy at room temperature is measured to be 222 MPa, and is enhanced to 265.8 MPa after extrusion at 420℃. The yield tensile strength （YTS） of AZ31 alloy at room temperature is measured to be 84 MPa, and is enhanced to 201 MPa after extrusion at 420℃. The effective improvements on mechanical properties result from the formation of the finer grains during extrusion and the finer particles precipitated by age treatment. The features of the microstructure evolution during hot extruded of AZ31 alloy are dislocation slipping on the matrix and occurrence of the dynamic recrystallization.     

Photocatalytic properties of TiO2 bonded active carbon composites prepared by SOL-GEL

Photocatalyst of TiO2 bonded active carbon (TiO2/AC), was prepared via sol-gel method from a mixture of TiO2 sol with active carbon. Post heat treatment was performed at 250℃ for 2h in air and then kept at 400℃ to 600℃ under a flow of nitrogen for 2 h. The TiO2/AC composites obtained were characterized by SEM, XRD, UVvis and BET. The photocatalytic activities of the TiO2/AC composites were studied in comparison with TiO2, AC, P-25 and a mixture of TiO2 and AC, respectively. The Ramnant rate of Rhodamine B absorbed by the active carbon is found to be almost 70 % and the remnant rates of the Rhodamine B decolorized by TiO2 and the mixture of TiO2 and the active carbon are 30% and 25%, respectively. However, nearly complete removal of Rhodamine B is observed for a TiO2/AC composite after 200 min under UV irradiation, which will take the P-25 commercial product 5h. Therefore, the TiO2/AC composite is much more effective in decolorization of aqueous Rhodamine B. In addition, the composite can be easily separated from solutions.     

Effect of heat-treatment on microstructure and properties of SiC particulate-reinforced aluminum matrix composite

The effects of solid solution and aging processing on the microstructures and mechanical properties of the multi-layer spray co-deposited 7090Al/SiCp composite were investigated. The experimented results show that fine grains and homogeneous microstructures can be obtained, the average grain size of the as-solid solution treated and as-aged composites after extrusion is under 3.0μm. A large amount of the Cu-rich phase particles form in the as-extruded samples, and solve into the matrix after solid solution treatment. After aging, the size of the precipitate phases, mainly MgZn2 and CuAl2 is less than 1.0 μm, which homogeneously distribute inside the grains and at the grain boundaries. The ultimate tensile strength of the composite treated at T6 state, i.e. solid solution treated at 475 ℃for 1 h then aged at 120 ℃ for 24 h, is up to 765 MPa.     

Influence of impurities on microstructure and mechanical properties of ZK60 magnesium alloy

The influence of impurity content on the microstructure and mechanical properties of ZK60 magnesium alloys was investigated by optical microscopy, scanning electron microscopy and tensile test. ZK60 alloys were prepared by changing holding time of alloy melt during semi-continuous casting in order to control the content of impurity elements. The alloy with lower purity content is found to have less second precipitates and larger grain size in the as-cast state. However, in the as-extruded state, reducing impurities brings about a decrease in grain size and an increase in yield strength from 244 MPa to 268 MPa, while the elongations in the as-extruded alloys with different contents of impurities are almost the same. After T5 treatment, impurity content is found to have more obvious effect on the yield strength of ZK60 alloy. The yield strength of ZK60-45 alloys with low impurity content is increased up to 295 MPa after T5 treatment.     

RECIPROCATING EXTRUSION OF IN SITU Mg_2Si REINFORCED Mg-Al BASED COMPOSITE

M92Si reinforced Mg-Al based composite with high amount o/silicon was prepared by permanent mould casting, and then extruded by reciprocating extrusion （RE） after the composite was processed by homogenization heat treatment. The effect of RE processing on the morphology and size of M92Si and the mechanical properties of the com- posite were investigated, to develop new ways to refine the M928i phase and improve its shape. The result showed that RE was very useful in refining the M92Si phase. The more the RE processing passes, the better the refining effect would be. Moreover, the uniform distribution of M928i phases would be more in the composite. After the composite was processed by RE for 12 passes, most M92Si phases were equiaxed, with granular diameter below 20 μm, and distributed uniformly in the matrix of the composite. The mechanical properties of the composite could be increased prominently by RE processing, and were much higher than that in the as-cast state. As the temperature rises, the tensile strength is reduced. For the composite RE processed for 12 passes, the tensile strength, yield strength, and elongation are 325.9 MPa, 211.4 MPa, and 3.3% at room temperature, whereas, 288.2 MPa, ,207.7 MPa, and 7.8%, respectively, at 150℃. In comparison with the properties at room temperature, the tensile strength and yield strength are high and only decrease by 11.6% and 1.8% at 150℃. The M928i reinforced Mg-Al based composite possesses good heat resistance at 150℃. The excellent resistance to effect of heat is attributed to the high melting tempera- ture and good thermal stability of fine Mg2Si phases, which are distributed uniformly in the composite, and effectively hinder the grain boundary gliding and dislocation movement.     

Synergistic effects of composition and heat treatment on microstructure and properties of vacuum die cast Al-Si-Mg-Mn alloys

The purpose of this study was to prepare high-quality Al-Si-Mg-Mn alloy with a good combination of strength and ductility employing the vacuum-assisted high-pressure die cast process. An orthogonal study of heat treatments was conducted to design an optimized T6 heat treatment process for both Al-10%Si-0.3%Mg-Mn and Al-11%Si-0.6%Mg-Mn alloys. The results demonstrate that no obvious blisters and warpage were observed in these two alloys with solid solution treatment. After the optimal T6 heat treatment of 530°C×3 h + 165°C×6 h, Al-11%Si-0.6%Mg-Mn alloy has better mechanical properties, of which tensile strength, yield strength and elongation reached 377.3 MPa, 307.8 MPa and 9%, respectively. The improvement of mechanical properties can be attributed to the high density of needle-like β″(Mg_5Si_6) precipitation after aging treatment and the fine and spherical eutectic Si particles uniformly distributed in the α-Al matrix.     

Preparation and photocatalytic activity of composite films containing clustered TiO2 particles and mineral tourmaline powders

The novel composite films containing clustered TiO2 particles and fine tourmaline particles on the surface of copper webs were prepared by the sol-gel method. The microstructures of the composite films were investigated by scanning electron microscopy （SEM）, and the photocatalytic activity of the films was evaluated by photocatalytic degradation of methyl orange, respectively. The results indicate that tourmaline particles can obviously influence the microstructures of TiO2 films and enhance the photocatalytic activity due to their spontaneous permanent polarity and high radiotechnology of far infrared. During preparing the composite films, the clustered TiO2 particles with lots ofnano-sized ladder layers can grow on the surface of fine tourmaline particles, the thickness of ladder layer is 10 nm, and the average diameter ofnano-sized TiO2 particles is 15 nm.     

Effect of Mn on microstructures and mechanical properties of Al-Mg-SiCu-Cr-V alloy

In order to improve the performances of the Al-Mg-Si-Cu-Cr-V alloy,various amounts of Mn(0-0.9wt.%) were added.The effect of this Mn on the microstructures and mechanical properties of Al-Mg-Si-Cu-Cr-V alloys in different states,especially after hot extrution and solid solution treatment,was systematically studied using scanning electron microscopy(SEM),energy dispersive spectroscopy(EDS),and mechanical tests at room temperature.The results show that 0.2wt.% Mn can both refine the as-cast microstructure of the alloy and strengthen the extrusion+T6 state alloy without damaging the plasticity badly due to the formation of Al 15(FeMn) 3 Si 2 and Al 15 Mn 3 Si 2 dispersoids.Compared with the extrusion+T6 state alloy without Mn addition,the ultimate tensile strength and yield strength of the alloy with 0.2wt.% Mn addition are increased from 416.9 MPa to 431.4 MPa,360.8 MPa to 372 MPa,respectively.The elongation of the extrusion+T6 state alloy does not show obvious change when the Mn addition is less than 0.5wt.%,and for the alloy with 0.2wt.% Mn addition its elongation is still as high as 15.6%.However,when over 0.7wt.% Mn is added to the alloy,some coarse,stable and refractory AlVMn and Al(VMn)Si phases form.These coarse phases can reduce the effect of Mn on the inhibition of re-crystallization;and they retain the angular morphology permanently after the subsequent deformation process and heat treatment.This damages the mechanical properties of the alloy.     

Electrical conductivity of Cu-Ag in situ filamentary composites

The electrical conductivity of Cu-10Ag in situ filamentary composite was studied during the deformation and annealing processes. The dependence of electrical resistivity of the deformed composites on the true strain presents a two-stage change with increase of the true strain. The intermediate heat treatment and the stabilized annealing treatment to the deformed composite promote the separation of Ag precipitate, and increase the electrical conductivity. The maximum conductivity of the composite experienced the stabilizing heat treatment can reach about 97% IACS with σb≥400 MPa at 550 ℃ annealing, and reach about 70% IACS with σb≥ 1 250 MPa at 300 ℃ annealing. The corresponded strength of the composite was reported. The microstructure reason for the changes of the conductivity was discussed.     

Research on Properties of Carbon Fiber/Epoxy Resin Composite Material by Microwave Curing

Microwave irradiation was used to reduce the curing time of carbon fiber/epoxy resin composite material.The properties of carbon fiber/epoxy resin composite material under microwave curing were investigated by thermogravimetry(TG),dynamic mechanical analysis(DMA),impact strength test and scanning electron microscope(SEM).The results show that composite materials patch have high thermal stability after microwave curing.The initial degradation temperature is 330.9℃,the maximum thermal decomposition rate is at 368.1℃.When the layer of composite materials patchis 4 layers,the dynamic mechanical properties are the best after microwave curing.The initial storage modulus is 43.2 GPa,increased 28.3 GPa and 27.1 GPa than 3 layers and 5 layers,the glass transition temperature(Tg)is 67.48℃,increased about 12 ℃than 3 layers and 5 layers.Microwave curing can significantly improve the infiltration capacity of epoxy resin,enhance interfacial bonding,and increase the impact strength of composite patch.Under microwave curing,the impact strength of 3,4,5-layers composite material patches increases 35.9%,6.4% and 15.1%,respectively than heating curing.The SEM analysis of impact fracture surface shows that microwave curing can improve the interface of carbon fiber and epoxy resin.     

Influence of Annealing Treatments on Microstructure and Mechanical Properties of an Extruded Mg AZ31/Al 7050 Laminate

Mg AZ31/A1 7050 laminate was fabricated by co-extrusion directly from the as-cast Mg AZ31 and Al 7050 billets. The influence of annealing temperature and annealing time on microstructure and mechanical behavior of the extruded Mg/Al laminate was systematically studied. Results show that annealing treatments at 250 ℃ for 3 h or at 350 ℃ for 3 h do not result in an obvious grain coarsening of Mg layer and cannot remove the heterogeneous structure. Annealing does not vary texture in the Mg layer, a large fraction of 0002//ND and a small fraction of 0002//TD, but the intensity of component 0002//ND weakens to some extent. Lamellar microstructure in the A1 layer remains after annealing at250 ℃ for 3 h or at 350 ℃ for 3 h. High fractions of the texture components S and cube exist in the extruded sample, and annealing treatment hardly changes their fractions. Post-annealing treatment will largely reduce yield strength of extruded plate and increase plasticity slightly. The yield strength drops from 302 MPa to 206 MPa after annealing at 250 ℃ for 3 h and to 141 MPa after annealing at 350 ℃ for 3 h. The elongation to fracture increases from 1.5% to 5.4% after annealing at 250 ℃ for 3 h and to 4.8% at 350 ℃ for 3 h. The corresponding mechanism was discussed.     

Microstructures and properties of 1.0%Al2O3/Cu composite treated by rolling

The 1.0%Al2O3/Cu （mass fraction） composite was prepared by hot pressing （HP）, then treated by rolling to get a full density. The microstructures and the micro area element distribution of the composite were analyzed by SEM. The density, electric conductivity and tensile strength were also investigated. The experimental results show that the alumina particles are more dispersed and become smaller through a single-pass rolling. The pore existing in the composite is eliminated or closed under the rolling force. The relative density increases from 98.4% to 99.2%. The electric conductivity increases from 88.9%IACS to 91.2%IACS. The tensile strength is increased by 47% from 300 MPa to 440 MPa.     

Copper-Ti3SiC2 composite powder prepared by electroless plating under ultrasonic environment

In this article, a new type of Cu-Ti3SiC2 composite powder prepared using the electroless plating technique was introduced. The initial Ti3SiC2 particles are 11 μm in diameter on an average. The Cu plating was carried out at middle temperature （62-65℃） with the application of ultrasonic agitation. The copper deposition rate was determined by measuring the weight gain of the powder after plating. It has been found that the pretreatment of Ti3SiC2 powder is very important to obtain copper nanoparticles on the surface of Ti3SiC2 The optimum procedure before plating aimed to add activated sites and the adjustment of the traditional composition of the electroless copper plating bath could decelerate the copper deposition rate to 0.8 gm/h. X-ray diffraction （XRD） indicates that the chemical composition of the plating layer is copper. SEM images show that the surface of the Ti3SiC2 particles is successfully coated with continuous copper layer. The wetting property between the copper matrix and Ti3SiC2 can be improved so as to increase the interfacial strength.     

Structural characterization and property of in-situ synthesized AZ91-Mg2Si composite

A new-type Mg2Si composite was prepared with Mg-9Al-1Zn （AZ91） alloy and vermiculite as raw materials by melt infiltration method. The results show that the microstructure of composite consists of a large amount of MgESi precipitates and a little amount of MgO embedded in α-Mg matrix. The Vickers hardness of the composite is obviously higher than that of matrix of AZ91 alloy. Moreover, the composite exhibits excellent compressive property. The ultimate compressive strength of the material is 290 MPa, the yield strength is 175 MPa, and the elongation is about 5%, which are higher than those of AZ91 alloy.