Papers by Keyword: Interface Reaction

Abstract: A comparative study of the surface contaminated layer formed by chemical reaction between ceramic-mold and titanium aluminum alloy castings or titanium alloy castings were carried out. The morphology, thickness and hardness of the surface contaminated layer were characterized by means of metalloscopy and microhardness measurement. The results show that surface contaminated layers formed between Ti-Al alloy castings and ceramic-mold, also formed between Ti alloy castings and ceramic-mold. The surface contaminated layers of Ti-Al alloy castings were continuous and compact, their thickness was about 0~90 μm. The surface contaminated layers of titanium alloy castings were not even, their thickness was 0~900 μm. Titanium alloy is more liable to react with the ceramic -mold than the Ti-Al alloy.

Abstract: The interfacial reaction between alloys and ceramic materials is an important factor to influence the quality and service performance of the turbine blade. In this paper, three typical height sections of 120mm, 160mm and 210mm were selected, and the interface reactions between DD6 single crystal superalloy and silica based ceramic cores were investigated by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS). The results showed that the infiltration degree of the melt alloy increases with the increase of reaction time. The thickness of the reaction layer could be over 0.3mm when the reaction time increased up to 70min. The main reasons of forming the infiltration layer were the infiltration of the Al element and the interfacial reaction between the Al element and the ceramic core. There formed an aluminum deficient layer on the metal surface because of the interface reaction between the alloy and the ceramic core. The dense layer formed by interfacial reaction on the surface of the core will cause some difficulties for core leaching. Keywords: DD6 single crystal superalloy; Silica based ceramic core; Interface reaction

Abstract: The interfaces between DZ40M directional solidified superalloy and ceramic mould (SiO₂-base core and Al₂O₃-base shell) was studied by scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). The results showed that there was a serious interface reaction between DZ40M and ceramic cores，which resulted in many reaction pits (~100μm deep), Si rich residue alloys and Zr rich subglobose oxides on the inner surface. And the interface reaction between DZ40M and ceramic shell induced a ~50μm of pink sand burning layer. The thermal analysis showed that the reactions between DZ40M and core or shell were similar: the active alloy constituents (Zr, Al, Ti and Cr) were oxidized and became oxides or solid solution with the core or shell components (SiO₂, Al₂O₃ or Fe₂O₃), but the interface characterization of DZ40M/core and DZ40M/shell was different because the shell had the main content of Al₂O₃ and impurity of Fe₂O₃, while those of the core were SiO₂ and CaO, respectively.

Abstract: In this paper, the contact interface between FGH96 superalloy melts and refractory slurry with corundum powder and silica sol at 1600°C with different soaking time in 10-240 min range was investigated. The morphology and composition of the contact interface were studied by optical microscopy (OM), scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). The results show that the reaction layer formed on the contact interface between the melting superalloy and the refractory slurry, and is mainly consist of Alumina and contains a small amount of other metal elements such as Ti and Cr. The reaction layer was not smooth on the micro level, and there was a peninsula-like structure protruding into the internal part of the melting superalloy on the reaction zone, and even started to fall off at some places to form islands. With the increase of soaking time, the reaction between melt of superalloy and refractory slurry increased gradually and the reaction layer began to combine with the refractory slurry substrate and form obvious interaction layered structure, resulting in the corrosion of refractory slurry substrate. With the soaking time over 120 min, the stable contact interface was destroyed. Thermodynamic calculation shows that the substitution reaction between Al in superalloy and SiO₂ in refractory slurry meets the thermodynamic conditions, and the reaction can proceed forward.

Abstract: Y₂O₃ doped SrZrO₃(SZY) powders were prepared according to a solid-state reaction method, which the raw materials contains SrCO₃, ZrO₂ and doped with 5 mol% Y₂O₃. And then the powders were used to make a green crucible shape by cold isostatic pressing. After that, the crucible was used to melt with TiNi alloy in the vacuum induction furnace with biscuit firing temperature of 900°C, and sintering temperature of 1750°C. The x-ray diffraction analysis (XRD), scanning electron microscope (SEM), and energy dispersive X-ray spectroscopy (EDS) were used to analysis the characterization of the Y₂O₃ doped SrZrO₃ power; microstructure of the crucible at different holding time under the 1750°C and the interfacial reaction between the crucible and the TiNi alloy. The results showed that the powders of Y₂O₃ doped SrZrO₃ were synthesized at 1200°C, and there was no obvious reaction layer and elements diffusion between the crucible and TiNi alloy. The ingot is easy to separate from the crucible after smelting.

Abstract: The investment casting technology is one of the major methods to produce the parts of the titanium due to its low production cost. However, the high activity of titanium melt gives rise to the requirement of high chemical stability of shell materials, to avoid or decrease the interfacial reaction between the mould and the melt. In this paper, a novel BaZrO₃ – coated Al₂O₃ shell was first introduced to the investment casting of titanium alloy. The grain size and baking temperature on the properties of the novel mould were investigated, and then the Ti6Al4V and TiNi alloys were successfully casted by means of this shell. The alloy-mould interaction was discussed. The results showed that the mould achieve high mechanical properties when the content of coarse powder was 50% after sintering 4 hours under 1500°C, and the BaZrO₃ coating exhibited an effective barrier to avoid the direct contact between the mould base material and the melt, the thickness of reaction layer of TiNi alloy was about 8 μm, and 17 μm to Ti6Al4V alloy, no refractory particles and elemental diffusion were observed inside the metal. This may imply that BaZrO₃ is a promising candidate material for the investment casting of titanium alloy.

Abstract: Ti₃Al based alloys are light and high-temperature materials, having potential wide applications in the aerospace and the aeronautical industries. Molten Ti is lively, and it is easy to react with the mold material during in the investment casting, and hence to form casting defects such as α contaminated layer in the metal near the surface and gas porosity, resulting in the deterioration of the surface quality and castings mechanical properties. Therefore, the mechanism of interfacial reaction between Ti₃Al-based alloys and mold is necessary to study. In this paper, the interface reaction samples of Ti-24Al-15Nb-1Mo alloy and ZrO₂ (Y₂O₃ stabilized) mold were prepared by actually investment casting. Optical microscopy, SEM, EMPA and micro-hardness tests were used to study the microstructures at metal side of interface, consider the element distribution and discuss the interfacial reaction mechanism. The results show that there is interface reaction between Ti-24Al-15Nb-1Mo alloy and ZrO₂ (Y₂O₃ stabilized) mold, and it belongs to the typical bilateral diffusion reaction. The elements of Zr, Y, O diffuse into molten metal, at the same time, the matrix elements spread to the oxide mold, then form interfacial reaction layer. It has been found that the interfacial reaction was not uniform in the whole interface. In the thick-wall of castings, the interfacial reaction layer was thicker, and in thin-wall, the interfacial reaction layer was thinner.

Abstract: In this work, the interface reaction between Al₂O₃ ceramic and Ag_70.5Cu_27.5Ti₂ brazing filler metal at 845-860°C was investigated. Based on the data of thermodynamics and kinetics, the Gibbs free energies of the main interface reactions in the real brazing system condition were calculated. But the values of normal equilibrium reaction condition and the real interface reaction brazing system were different; and the main influential factor was the brazing temperature, and the system vacuum of brazing condition can lead the change of equilibrium constant (Kα). The results revealed that the high temperature and vacuum active brazing is a non-equilibrium interface reaction especially to titanium alloy, the vacuum and alloy liquid solution are beneficial to the brazing process, and the by-product formation of titanium-oxygen are affected by the diffusion process.

Abstract: CNTs/Al composites were fabricated by high energy ball milling. The phase structure and consti- tuent of the preparation process were analyzed. The interface reaction and the formation process of the interface reaction product Al₄C₃ were discussed by thermodynamics and kinetics. The result shows that no Al₄C₃ can be found in Al-CNTs composite powders fabricated by high energy ball milling. Al₄C₃ exists in the inter- face after pressureless sintering. And no appreciable amount of Al₄C₃ was observed in CNTs/Al composites directly by powder metallurgy. It shows that high energy ball milling can benifit the interface reaction. And the purified CNTs, never milled, is stable in the preparation process of CNTs/Al composites by powder metallurgy.

Abstract: The necessity of preserving resources and to reduce environmental pollution makes light weight concepts highly interesting for the transportation market, with light weight being essential for newly developed electric and hybrid vehicles. However, some components cannot be replaced only by aluminium, but need to be combined with steel in order to achieve the desired mechanical characteristics. Therefore, there is great interest in developing processes to manufacture aluminium/steel hybrid structures that present a good bond.In the present work a range of processing conditions for improving the bond strength between S355J2H steel inserts and AlSi7Mg casting alloy were investigated. Before casting, different chemical, thermal and mechanical treatments were applied to the steel insert: As-received condition, preheating, shot blasting, pickling, hot dip aluminizing, hot dip galvanizing, zinc coating and nickel/copper plating. The steel/AlSi7Mg interfaces were characterized by optical microscopy (LOM), scanning electron microscopy (SEM) and x-ray diffraction (XRD). Special attention was paid to the presence of defects, formation of oxides and/or intermetallic phases in the reaction zone. The interface shear strength has been assessed by the push-out test, and the results have been correlated with microstructural observations at the interfaces. Combinations of different insert treatments were also investigated.