Powder injection molding of pure titanium

An improved wax-based binder was developed for powder injection molding of pure titanium. A critical powder loading of 69 vol.% and a pseudo-plastic flow behavior were obtained by the feedstock based on the binder. The injection molding, debinding, and sintering process were studied. An ideal control of carbon and oxygen contents was achieved by thermal debinding in vacuum atmosphere （10^-3 Pa）. The mechanical properties of as-sintered specimens were less than those of titanium made by the conventional press-sintering process. Good shape retention and ±0.04 mm dimension deviation were achieved.

KINETIC MODEL FOR POWDER INJECTION DESULFURIZATION

The kinetic model for desulfurization using CaO-based powder injection has been proposed, which accords with the actual process of the experiment. For the model, a comparison between CaO-based flux and Mg-based flux was made and the results show that the desulfurization rate of the Mg-based flux is far more than that of CaO-based flux. On the basis of the model calculation, on comparison of CaO-CaF2 flux and calcium aluminate flux, the desulfurization rates of the two fluxes are close to each other. In addition, the effects of some operational factors on the kinetics of desulfurization are discussed.

Powder injection molding of Fe-Ni soft magnetic alloys

With miniaturization and complication of the shape of electronic devices in recent years, powder injection molding (PIM) seems to be a suitable process for fabricating the higher performance soft magnetic components. In this paper, high quality Fe-50Ni soft magnetic alloy was fabricated by PIM with carbonyl iron and nickel, and the effect of sintering process on its microstructure and magnetic properties were investigated. The mechanical and magnetic properties can be obviously improved by increasing the sintering temperature or using the hydrogen atmosphere instead of high vacuum, which causes by the increase of grain size and the densification. At the optimum sintering conditions, the PIM Fe-50Ni soft magnetic alloy with high properties are obtained, whose relative density, tensile strength, Bm, Hc, μm are 97%, 465 MPa, 1.52 T, 16.62 A·m-1, 42.5 mH·m-1, respectively.

Effects of heat treatment on the properties of powder injection molded AlN ceramics

The effects of two different heat-treatment atmospheres,nitrogen atmosphere and reducing nitrogen atmosphere with carbon,on the properties of Y2O3-doped aluminum nitride（AlN） ceramics were investigated.The AlN powder as a raw material was synthesized by self-propagating high-temperature synthesis（SHS） and compacts were fabricated by employing powder injection molding technique.The polymer-wax binder consisted of 60 wt.% paraffin wax（PW）,35 wt.% polypropylene（PP）,and 5 wt.% stearic acid（SA）.After the removal of binder,specimens were sintered at 1850°С in nitrogen atmosphere under atmospheric pressure.To improve the thermal conductivity,sintered samples were reheated.The result reveals that the heat-treatment atmosphere has significant effect on the properties and secondary phase of AlN ceramics.The thermal conductivity and density of AlN ceramics reheated in nitrogen gas are 180 W·m^-1·K^-1 and 3.28 g·cm^-3 and the secondary phase is yttrium aluminate.For the sample reheated in reducing nitrogen atmosphere with carbon,the thermal conductivity and density are 173 W·m^-1·K^-1 and 3.23 g·cm^-3,respectively,and the secondary phase is YN.

Preparation of high nitrogen and nickel-free austenitic stainless steel by powder injection molding

High nitrogen and nickel-free austenitic stainless steel has received much recognition worldwide because it can solve the problem of ＂nickel-allergy＂ and has outstanding mechanical and physical properties. In this article, 0Cr17Mn11Mo3N was prepared by powder injection molding （PIM） technique accompanied with solid-nitriding. The results show that the critical solid loading can achieve up to 64vol% by use of gas-atomized powders with the average size of 17.4 μm. The optimized sintefing conditions are determined to be 1300℃,2 h in flowing nitrogen atmosphere, at which the relative density reaches to 99% and the N content is as high as 0.78wt%. After solution annealing at 1150℃for 90 rain and water quench, the 0.2% yield strength, ultimate tensile strength （UTS）, elongation, reduction in area, and hardness can reach as high as 580 MPa, 885 MPa, 26.0%, 29.1%, and Hv 222, respectively.

Microstructure and properties of nano-TiN modified Ti(C,N)-based cermets fabricated by powder injection molding and die pressing

Powder injection molding （PIM） and die pressing were employed to fabricate nano-TiN modified Ti（C,N）- based cermets. The shrinkage behavior, microstructure, porosity, and mechanical properties of the samples with and without nano-TiN addition fabricated by PIM and die pressing were analyzed. It is demonstrated that for either PIM or die pressing, the porosities are obviously reduced, the mechanical properties are significantly improved after adding nano-TiN, and the hard particles are refined; the rim phase thickness obviously becomes thinner, and the number of dimples in fracture also increases. Compared the samples fabricated by die pressing, it is difficult for PIM to obtain dense Ti（C,N）-based cermets. Due to the too much existence of pores and isolated carbon, the mechanical properties of the sintered samples by PIM are inferior to those of the sintered ones by die pressing.

Sintering Mechanism of Stainless Steel in Powder Injection Molding

Stainless steel samples were made by Powder injection Molding (PIM) process with-400 mesh powder in order to investigate the sintering mechanism in this system and develop the PIM of stainless steels. The process included mixing, injection molding, debin- ding and sintering. Neck growth model was used to analyze the sintering mechanism. The results show that lattice (volume) diffusion is the main mechanism in the sintering process, the products with higher density (>95%) and properties are obtained. At lower temperatures, grain boundary diffusion may play a role in the sintering densification.

Powder transport behavior in RH degasser with powder injection through up snorkel: a transient numerical model

A transient numerical model was established to predict the dispersion,distribution,and circulation behavior of the powder injected through the up snorkel in a Ruhrstahl–Heraeus(RH)degasser.The effects of the powder diameter,the lifting gas flow rate,and the powder injection rate on the powder transport were investigated.Local powder concentration was measured by a cold model.The results showed that the predicted powder concentration agreed well with the measured.The powder injection process is divided into three periods,named dispersion period,aggregation and circulation period,and dynamically stable period according to the powder transport behavior.The powder diameter has a great effect on the particle dispersion.When the particles size changes from 30 to 500μm,the powder dispersion characteristic index changes from 0.110 to 0.741,and the ladle top zone powder mass ratio changes from 0.118 to 0.685.The powder circulation mass flow rate increases to 101.0 kg min^(-1)(150μm)and then decreases to 46.6 kg min^(-1)(500μm).Powders with a diameter of more than 220μm can change the steel flow mode in the RH degasser.Increasing the lifting gas flow could slightly improve the powder dispersion.Variation in the powder injection rate has almost no effect on the powder dispersion.

Physical modelling of particle transport phenomenon and vibration behavior of converter with bottom powder injection

A cold model of top-bottom blown converter was set up to study the particle transport phenomenon and vibration performance of converter with bottom powder injection.The effect of bottom blowing flow rates,tuyere diameters,arrangements,and powder to gas mass ratios on powder distribution and furnace body vibration was investigated.The results show that the bottom injection parameters and modes have significant effects on the particle transport behavior and furnace vibration.The powder dispersion uniformity and furnace vibration increase with the increase in bottom blowing tuyere diameters.In the lower range of bottom blowing flow rates and powder to gas mass ratios,the powder dispersion uniformity is improved with the increase in them.However,in the higher range,the excessive furnace vibration leads to reduction in uniformity in powder dispersion.When the bottom blowing tuyeres arrange at double arrangement of 0.5R(R refers to the radius of the bottom)distance between tuyere and center of bath bottom,the converter has optimal particle transport behavior and vibration performance.The vibration law of converter with bottom powder injection was revealed by deducing the empirical formulas of furnace vibration maximum amplitude.The vibration intensity is affected by Froude number,powder to gas mass ratio,and tuyere arrangement.

Simulation on Hot Metal Dephosphorization by Powder Injection in Torpedo-Car

Powder injection is widely used in hot metal pretreatment. The kinetic analysis of refining process shows that the reagent utilization and pretreatment efficiency are determined by the penetration ratio of powder into metal, the residence time of powder in the metal bath, as well as the uniform mixing time of the bath. The characterization of these parameters is studied with water model experiment, and, a mathematical model is developed for hot-metal dephosphorization in torpedo car. Water-model experiment results and industrial data are used to determine the model parameters and verify this model, the results show that the prediction from the model agrees well with practical results.

Corrosion resistance of powder injection moulded titanium in physiologic serum and artificial saliva

Most of dental implants are made from titanium or titanium based alloys.However, one of the drawback of such implants is high cost due to the technological difficulties in casting method or machining.In this work, powder injection moulding（PIM） method has been used in order to explore lower cost implants without minimising the biocorrosion resistance of the titanium.Corrosion resistance of titanium specimens, produced by powder injection moulding method（PIM-Ti）, in physiologic serum and artificial saliva was investigated.Commercially pure bulk Ti（CP-Ti） was used as control sample.Surface oxidation was also carried out to both PIMTi and CP-Ti samples.Microstructure and corrosion resistance were investigated using microhardness, X-ray diffraction（XRD）, scanning electron microscopy（SEM） and potentiodynamic polarization experiments.Resulting microstructure of PIM-Ti samples contained porosity as compared to CP-Ti control samples.Microhardness of PIM-Ti samples varied with varying applied load whereas it was free from applied load for CP-Ti control samples.Polarisation measurements and SEM analysis revealed that corrosion behaviour of PIM-Ti was reasonably as good as CP-Ti both in as-produced and oxidized conditions in physiologic serum and artificial saliva in spite of its porous structure.

Clinical Non-inferiority Trial on Treatment of Coronary Heart Disease Angina Pectoris of Xin-blood Stasis Syndrome Type with Lyophilized Salvia Salt of Lithospermic Acid Powder for Injection

Objective： To evaluate the effectiveness and safety of lyophilized Salvia salt of lithospermic acid powder for injection （SSLA） in treating coronary heart diseases angina pectoris （CHD-AP） of Xin-blood stasis syndrome type, and to conduct the non-inferiority trial with Danshen injection （丹参注射液, DSI） as positive control. Methods： An non-inferiority clinical layered, segmented, randomized, and blinded trial on three parallel and multiple centered groups was conducted in 480 patients with stable effort angina grade Ⅰ , Ⅱand Ⅲ, who had two or more times of attack every week. The 240 patients in test group A were treated with SSLA 200 mg added in 250 ml of 5% glucose solution for intravenous dripping every day; the 120 patients in test group B were treated with SSLA but the dosage doubled; and the 120 patients in the control group were treated with DSI 20 ml daily in the same method as SSLA was given. The clinical effectiveness and safety were evaluated after the patients were treated for 14 days. Results： The results showed that the markedly effective rate in test groups A, B and control group was 37.45 %, 36.75 % and 30.09 % respectively, while the total effective rate in them was 88.09%, 89.74% and 67.26% respectively. Statistical significance was shown in comparisons of the therapeutic effect between control group with test group A and test group B, with that in the two test groups superior to that in the control group, and non-inferiority trial showed eligibility （P〈0.01）. Adverse reaction appeared in 8 patients in the test groups and 2 in the control group. Conclusion： SSLA has definite therapeutic effect in treating patients with CHD-AP, with its effect not inferior to that of DSI, and no evident toxic-adverse reaction.

Injection molding of micro-porous titanium alloy with space holder technique

The powder space holder （PSH） and powder injection molding （PIM） methods have an industrial competitive advantage because they are capable of the net-shape production of micro-sized porous parts. In this study, micro-porous Ti6Al4V alloy （Ti64） parts were produced by the PSH-PIM process. Ti64 alloy powder and spherical polymethylrnethacrylate （PMMA） particles were used as a space holder material. After molding, binder debinding was performed by thermal method under inert gas. Debinded samples were sintered at 1250℃ for 60min in a vacuum （10-4 Pa）. Metallographic studies were conducted to determine densification and the corresponding microstructural changes. The surface of sintered samples was examined by SEM. The compressive stress and elastic modulus of the rificro-porous Ti64 samples were determined. The effects of fraction of PMMA on the properties of sintered micro-porous Ti64 alloy samples were investigated. It was shown that the fraction of PMMA could be controlled to affect the properties of the Ti alloy.

Influence of binder composition on the rheological behavior of injection-molded microsized SiC suspensions

The influence of four kinds of binders consisting of paraffin wax （PW）, random-polypropylene （RPP）, high-density polyethylene （HDPE）, and stearic acid （SA） on the theological behavior of injection-molded SiC feedstocks was investigated over a temperature range of 150℃ to 180℃ and a shear rate range of 4 s^-1 to 1259 s^^-1. The results showed that all the feedstocks exhibited pseudoplastic flow behavior. The wax-based binder of multipolymer components （PW-RPP-HDPE） exhibited better comprehensive rheological properties compared with the binder of monopolymer components （PW-RPP or PW-HDPE）. The addition of 5wt% SA to the binder could reduce the viscosity of the feedstock but enhance the rheological stability by improving the wettability between the binder and the SiC powder. The binder of 65wt% PW ＋ 15wt% HDPE ＋ 15wt% RPP ＋ 5wt% SA was found to be a better binder for microsized SiC injection molding.

Rheologic behavior and PIM processing of WC-TiC-Co powder feedstock

An improved wax-based binder was developed for the powder injection molding (PIM) of WC-TiC-Co cemented carbides. The critical powder loading and the rheologic behavior of the feedstock were determined. It was found that the critical powder loading could achieve up to 62.5% (volume fraction) and the feedstock exhibited a pseudo-plastic flow behavior. The injection molding, debinding and sintering processes were studied. The dimension deviation of the sintered samples could be controlled in the range of ±0.2% with the optimized processing parameters and the mechanical properties were better than or equivalent to those of the same alloy made by conventional press-sintering process.

Rheologic behavior and PIM processing of WC-TiC-Co powder feedstock

An improved wax-based binder was developed for the powder injection molding(PIM) of WC-TiC-Co cemented carbides. The critical powder loading and the rheologic behavior of thefeedstock were determined. It was found that the critical powder loading could achieve up to 62.5percent (volume fraction) and the feedstock exhibited a pseudo-plastic flow behavior. The injectionmolding, debinding and sintering processes were studied. The dimension deviation of the sinteredsamples could be controlled in the range of + -0.2 percent with the optimized processing parametersand the mechanical properties were better than or equivalent to those of the same alloy made byconventional press-sintering process.

Mathematical Modeling of the Vacuum Circulation Refining Process of Molten Steel

The available studies in the literature on mathematical modeling of the vacuum circulation (RH) refining process of molten steel have briefly been reviewed. The latest advances obtained by the author with his research group have been summarized. On the basis of the mass and momentum balances in the system, a new mathematical model for decarburization and degassing during the RH and RH KTB refining processes of molten steel was proposed and developed. The refining roles of the three reaction sites, i.e. the up snorkel zone, the droplet group and steel bath in the vacuum vessel, were considered in the model. It was assumed that the mass transfer of reactive components in the molten steel is the rate control step of the refining reactions. And the friction losses and drags of flows in the snorkels and vacuum vessel were all counted. The model was applied to the refining of molten steel in a multifunction RH degasser of 90 t capacity. The decarburization and degassing processes in the degasser under the RH and RH KTB operating conditions were modeled and analyzed using this model. Besides, proceeded from the two resistance mass transfer theory and the mass balance of sulphur in the system, a kinetic model for the desulphurization by powder injection and blowing in the RH refining of molten steel was developed. Modeling and predictions of the process of injecting and blowing the lime based powder flux under assumed operating modes with the different initial contents of sulphur and amounts of powder injected and blown in a RH degasser of 300 t capacity were carried out using the model. It was demonstrated that for the RH and RH KTB refining processes, and the desulphurization by powder injection and blowing in the RH refining, the results predicted by the models were all in good agreement respectively with data from industrial experiments and practice. These models may be expected to offer some useful information and a reliable basis for determining and optimizing the technologies of the RH and RH KTB refining and desulphurization by powder injection and blowing in the RH refining and for controlling the processes.

Research on Oxygen Sensor for Metallurgical Process

A new technique for manufacture of the oxygen sensor used for metallurgical process has been developed.The powder of MgO-PSZ was prepared by coprecipitation.The MgOPSZ tube was prepared by powder injection molding(PIM).The final sintered tube was assembled into oxygen cell,then tested in laboratory and on RH vessel.The results showed that the thermal shock resistance of MgO-PSZ matrix is strong enough for determining the active oxygen concentration in steel melt.The reproducibility of the EMF measurement is very good.The structure of the tube has been analysed by means of SEM and XRD.In addition,the characteristics such as the density and phase ratio in the product were compared with that of Shijiazhuang Maple Wood Sensor Company s product.

Microstructural Feature of As-cast A-356 Alloy Modifiers with the Addition of SrO

To explore the effect of strontium on the structure of as-cast A356 alloy, the strontium was incorporated to the alloy by metallothermic reduction of SrO where the mineral was added to the melt through the submerged powders injection technique. The evaluation of the modification of the eutectie silicon and the chemical analysis of samples were done using optical microscopy （OP） and inductively coupled plasma （ICP）, respectively, while microstructural analyses by scanning electron microscopy （SEM）, and the injection time was variable. Magnesium was added to the melt to increase the reactivity and reduce the surface tension of the molten aluminum. It was possible to increase the strontium content from 0 to 0.027% after 20 minutes treatment. This concentration was sufficient to bring about full modification structure of eutectic silicon of as cast alloy A 356 and the acceptable quality metallurgical of alloy.