金属粉末注射成形钛合金工艺研究

为了探究保障最终产品性能满足ASTM标准的粉末注射成形工艺,本文采用金属粉末注射成形方法,以德国Basf公司提供的喂料为原料,通过对注射参数优化获取1组最优注射工艺参数,用于后续脱脂及烧结工艺.利用拉伸、弯曲等力学实验,扫描电镜、金相光学显微镜等表征方法对材料的力学性能及微观结构进行表征,研究了注射、脱脂和烧结工艺参数...     

新型金属注射成形催化脱脂型粘结剂的催化快速分解研究

催化脱脂是目前MIM技术领域新的发展方向,研究了新型金属注射成型催化脱脂型粘结剂的催化快速分解,研究结果表明,该催化脱脂型粘结剂在以HNO3为催化剂进行催化脱脂时,注射成形坯经3－4h催化脱脂后,脱脂坯内部已形成大量的连通孔道,脱脂时间,脱脂温度以及 不同粘结剂组成影响催化脱脂效果。     

Preparation of nanoporous titanium oxide films by electrochemical anodic oxidation

We have investigated the conditions of the formation of tubular layers of nanoporous TiO₂ (NPTO) by the anodic oxidation of Ti in a 1% ammonium fluoride solution in ethylene glycol. The results demonstrate that increasing the anode current density and anodization time increases the nanotube diameter. A model has been proposed for the formation of tubular NPTO layers. The model builds on the concept of anisotropic Ti etching. The rate of the formation of the tubular structure of TiO₂ has been shown to be limited by the oxide film growth rate under the conditions of this study.     

金属注射成形水溶性粘结剂的研制

研究了一种以ＰＥＧ为主要组分的粘结剂,考察了它对Ｆｅ－２Ｎｉ粉末注射成形的适应性。实验结果表明：该粘结剂体系混合和注射工艺性能好,φ（Ｆｅ－２Ｎｉ）粉末装载量可达５５％,水中脱脂速度可达０．８－２ｍｍ／ｈ。     

Replication of metal microstructures by micro powder injection molding

In this paper, a study on the production of 316L stainless steel microstructures by μPIM (powder injection molding) is presented. Two types of mold inserts were used and the molding was conducted on a conventional injection molding machine. Based on the characteristics of the mold inserts and the feedstock, suitable processing parameters were selected. Some requirements for the production of the microstructures are discussed. For example, a relatively high mold temperature, high injection pressure and holding pressure were required. The study showed that 316L stainless steel microstructures of φ100 × 200 μm can be injection molded, but there were incomplete filling and demolding problem in the case of smaller microstructures of φ60 × 191 μm. The molded parts were successfully debound and sintered.     

Isotropic forming of porous structures via metal injection molding

Metal injection molding (MIM) is a near net-shape process that offers the unique ability to manufacture porous components with homogeneous porosity, pore structure and permeability. MIM is a process that can significantly reduce production cost when large quantities of components with complex shape need to be delivered. In this study, MIM is used to produce porous 316L stainless steel structure from both water and gas atomized powders. The porous components made by MIM were characterized to evaluate their suitability for small pore structure applications. The porous structures were analyzed for porosity, pore size, permeability, and thermal conductivity as a function of powder type and processing conditions. A typical MIM powder (<20 μm) processed at 50 vol% loading in a binder system produced a uniform pore structure with a permeability of less than 1⋅10^{− 13} m² and a maximum pore radius of less than 5 μm. Water-atomized powder proved to be better suited for low-solids-loading metal injection molding (<50 vol% loading) since its irregular shape provided greater strength and fewer defects during the molding and debinding process steps. Measurements of thermal conductivity show that the water-atomized powder had less thermal conductivity (∼2 W/m-K) than the gas-atomized powder (∼3 W/m-K). This study shows that MIM is a suitable process that can be used to manufacture functional porous structures that require isotropic pore size and complex shape.     

Titanium oxide films produced on commercially pure titanium by anodic oxidation with different voltages

Titanium oxide films produced on commercially pure Ti by anodic oxidation with different voltages were analyzed. Anodic oxidation was carried out at room temperature using 1.4 M H₃PO₄ electrolyte and a platinum counter-electrode, in potentiostatic mode under the following conditions: 50 V, 100 V, 150 V, 200 V and 250 V. It was observed that porous titanium layers were formed at all voltage values but morphological differences were observed. Initially, the film was thin but with increasing voltage it broke down locally and porous regions became evident due to the dielectric breakdown. The porosity and the pore size increased with the increasing voltage. The surface morphology in samples formed with 200 V had substantially different porous structures than those formed with other voltage values. The anodic film surface displayed pores and craters formed on the relatively flat ground oxide surface. AFM images showed that higher voltages produced thicker titanium oxide films.     

Structure, morphology and fibroblasts adhesion of surface-porous titanium via anodic oxidation

Surface-porous titanium samples were prepared by anodic oxidation in H₂SO₄, H₃PO₄ and CH₃COOH electrolytes under various electrochemical conditions. X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDX) were employed to characterize the structure, morphology and chemical composition of the surface layer, respectively. Closer analysis on the effect of the electrochemical conditions on pore configuration was involved. It can be indicated that porous titania was formed on the surface layer, and the pore configuration was influenced by electrolyte composition and crystal structure of the titania. The fibroblast cells experiment showed that anodic oxidation of titanium surface could promote fibroblast adhesion on Ti substrate. The results suggested that anodic oxidation of Ti in CH₃COOH was suitable to obtain surface-porous titanium oxides layers, which might be beneficial for better soft tissue ingrowths.     

Increased reactivity and in vitro cell response of titanium based implant surfaces after anodic oxidation

In the quest for improved bone growth and attachment around dental implants, chemical surface modifications are one possibility for future developments. The biological properties of titanium based materials can be further enhanced with methods like anodic polarization to produce an active rather than a passive titanium oxide surface. Here we investigate the formation of hydroxide groups on sand blasted and acid etched titanium and titanium–zirconium alloy surfaces after anodic polarization in an alkaline solution. X-ray photoelectron spectroscopy shows that the activated surfaces had increased reactivity. Furthermore the activated surfaces show up to threefold increase in OH^? concentration in comparison to the original surface. The surface parameters S_a, S_ku, S_dr and S_sk were more closely correlated to time and current density for titanium than for titanium–zirconium. Studies with MC3T3-E1 osteoblastic cells showed that OH^? activated surfaces increased mRNA levels of osteocalcin and collagen-I.     

Sintering of 17-4PH stainless steel feedstock for metal injection molding

The sintering behavior of 17-4PH stainless steel feedstock for metal injection molding was investigated in the temperature range of 650-1050 °C. Effects of sintering conditions, such as sintering temperature and sintering atmosphere, were examined. Results showed that when sintered in the hydrogen/nitrogen atmosphere, the 17-4PH feedstock was oxidized over the temperature range of investigation. The degree of oxidization increased with the sintering temperature. The main oxidization product was Cr₂O₃ as revealed by X-ray diffraction and composition analysis. The oxidation can be avoided by sintering in vacuum or argon atmosphere.     

Nano-structured TiO2 films by plasma electrolytic oxidation combined with chemical and thermal post-treatments of titanium, for dye-sensitised solar cell applications

This paper demonstrates a new method to grow nano-structured TiO₂ over a plasma electrolytically oxidised titanium surface. Microstructural characterisation by employing a variety of transmission electron microscopy techniques was carried out to explore the nano-scale structural changes due to the alkaline and thermal treatments. Photovoltaic performance was measured and this revealed the effect of microstructural changes. Such coatings can be considered potential candidates for the electrode material in a dye-sensitised solar cell (DSSC). The experimental results show that a titania layer with a 3D network ‘nano-flaky’ surface can be successfully prepared. The obtained nano-flakes are around 100 to 200 nm across and have a thickness of less than 10 nm. These completely cover the outermost surface as well as the inner pores and voids. The formed nano-flaky structure is amorphous and provides a larger surface area for dye absorption to increase the efficiency of assembled DSSC. Thermal annealing treatment causes the transformation of the amorphous nano-flakes into anatase nano-crystallites and further enhances the photovoltaic efficiency of the assembled DSSC.     

Microstructure and mechanical properties of titanium components fabricated by a new powder injection molding technique

A powder injection molding (PIM) binder system has been developed for reactive metals such as titanium that employs an aromatic compound as the primary component to facilitate easy binder removal and mitigate problems with carbon contamination. In the study presented here, we examined the densification behavior, microstructure, and mechanical properties of titanium specimens formed by this process using naphthalene as the principle binder constituent. In general, it was found that tensile strengths could be achieved comparable to wrought titanium in the PIM-formed specimens, but that maximum elongation was less than expected. Chemical and microstructural analyses indicate that this process does not add oxygen to the material,suggesting that the use of higher purity powder and further process optimization should lead to significant improvements in ductility.     

Effect of hot water and heat treatment on the apatite-forming ability of titania films formed on titanium metal via anodic oxidation in acetic acid solutions

Titanium and its alloys have been widely used for orthopedic implants because of their good biocompatibility. We have previously shown that the crystalline titania layers formed on the surface of titanium metal via anodic oxidation can induce apatite formation in simulated body fluid, whereas amorphous titania layers do not possess apatite-forming ability. In this study, hot water and heat treatments were applied to transform the titania layers from an amorphous structure into a crystalline structure after titanium metal had been anodized in acetic acid solution. The apatite-forming ability of titania layers subjected to the above treatments in simulated body fluid was investigated. The XRD and SEM results indicated hot water and/or heat treatment could greatly transform the crystal structure of titania layers from an amorphous structure into anatase, or a mixture of anatase and rutile. The abundance of Ti–OH groups formed by hot water treatment could contribute to apatite formation on the surface of titanium metals, and subsequent heat treatment would enhance the bond strength between the apatite layers and the titanium substrates. Thus, bioactive titanium metals could be prepared via anodic oxidation and subsequent hot water and heat treatment that would be suitable for applications under load-bearing conditions.     

Rapid hard tooling by plasma spraying for injection molding and sheet metal forming

Amidst the harsh competition over the development of new products around the world, rapid prototyping, especially rapid tooling methods have received widespread attention. Amongst the rapid hard tooling methods, thermal spraying can manufacture metal molds without limitation of pattern size. However, it has the disadvantage that only soft metals with low melting points such as zinc alloy can be sprayed to original mold, such as a rapid prototyping model or a natural material pattern, due to their lack of heat resistance and shrinkage of spray metals. So the wear resistance of spray tool is poor, it can be used only for trial or small-lot production. In this study, attempts were made to improve the heat resistance by using composite materials made of ceramic and metal powders as the sprayed original mold materials, and using stainless steel, tungsten carbide alloy, iron–nickel–chromium alloy with excellent wear resistance as spraying materials, respectively. The results show that injection molding spray mold and sheet metal forming spray die can be made by transferring from natural patterns and rapid prototyping models. As the durability and dimensional accuracy of the sprayed tools has sharply improved, the tools can be used for mass production.     

Application of metal injection molding process to fabrication of bulk parts of TiAl intermetallics

In the present study, a metal injection molding (MIM) process was applied to the fabrication of bulk parts of TiAl intermetallics, and effects of sintering parameters on densification of fabricated parts were investigated. The specimens sintered at 1350 °C showed about the same densification as the ones sintered at 1400 °C, while grains and pores were finer, and thus 1350 °C was chosen as the sintering temperature. In the sintered specimens after debinded in an H₂ atmosphere, Al₂O₃ precipitates were observed around pores. The densification decreased with increasing heating rate up to the sintering temperature. It was also found that the sintering time increased the densification without grain coarsening. The optimal heating rate was found to be 3 °C/min, and the densification reached a near-full level of 98.8% when sintered at 1350 °C for 30 h. These findings suggested a useful idea to successfully fabricate TiAl intermetallic parts by the MIM process.