Interactions between TiAl and ZrO2 Face Coat during Centrifugal Investment Casting

2014 ◽  
Vol 1044-1045 ◽  
pp. 59-62
Author(s):  
Yan Fei Chen ◽  
Yuong Chen ◽  
Jiang Ping Tu ◽  
Shun Qi Zheng
Keyword(s):  
Investment Casting ◽  
Ceramic Shell ◽  
Tial Alloys ◽  
Good Oxidation Resistance ◽  
Specific Strength ◽  
High Specific Strength ◽  
The Face ◽  
Shell Mould ◽  
Near Net Shape ◽  
Face Coat

γ-TiAl alloys are emerging as potential light-weight, high-temperature structural materials and possess wide capacities of engineering applications in aeronautics, space and automobile industries because of their low density, high specific strength and specific modulus, good oxidation-resistance and creep-resistance. Investment casting is introduced to complex TiAl net-shape or near net-shape components. In this research, ZrO2 (CaO stabilized) was chosen as the face coat materials for the investment casting of TiAl alloys. The present study mainly focuses on the fabrication of ceramic shell mould for TiAl investment casting. Optimisation of reducing the stress in cast-mould system was carried out. The processing technology of the invented ceramic shell moulds was successfully verified in the investment casting of prototype TiAl parts. The interfacial reaction between TiAl alloys and ZrO2 ceramic mould was analyzed using OM, SEM, EDS and XRD. The experimental results showed that, when the rotation speed is 200 rpm and 400 rpm, the thickness of reaction layer is about 5μm and 20μm, respectively.

Toughening of Ceramic Shell Mould with Rice Husk Fiber (CSm-RH) to Improve Strength Property and Mould Performance

2021 ◽  
Vol 2 (2) ◽  
Author(s):  
Noor Hasliza Kamarudin ◽  
◽  
Zawati Harun ◽  
Rosniza Hussain ◽  
Mohd Riduan Jamalludin ◽  
...  
Keyword(s):  
Rice Husk ◽  
Investment Casting ◽  
Ceramic Body ◽  
Ceramic Shell ◽  
Adhesion Properties ◽  
Ceramic Structure ◽  
Green Strength ◽  
Body Strength ◽  
Shell Mould ◽  
Casting Industry

For ages, ceramic shell mould (CSm) have been extensively applied in investment casting industry. The formation of CSm requires multiple steps of dipping, layering drying and firing stages. The later steps are very crucial as the solidification thin layer CSm that consist of loose ceramic particles easily cracks when exposed to the higher thermal effect. The inclusion of fiber or any reinforces phases is able to enhance fired ceramic body and also strengthen the green ceramic structure. Thus, the feasibility of rougher NaOH treated rice husk fiber (RHT) prior embedded into composited structure has shown a significant CSm improvement by induced a better adhesion properties and larger bonding area with brittle ceramic matrix, resulted in increased green strength (1.34 MPa) and fired body strength (4.32 MPa). Owing to the decomposed of lignin layer in CSm with untreated rice husk fiber (CSm-RHU) exhibited a higher porosity that provide a better permeation paths of air flow during molten metal pouring as increased 30 % from the standard CSm permeability, giving an enormous benefit for investment casting cooling process. Overall, the incorporation of RHT fiber in a CSm matrix of both green and fired body governed in toughening of brittle ceramic body, hence avoid failure to the casting mould.

Permeable Rice Husk Fibre Shell Mould System

2013 ◽  
Vol 372 ◽  
pp. 331-335 ◽  
Author(s):  
Zawati Harun ◽  
Noor Hasliza Kamarudin ◽  
Muhamad Zaini Yunos
Keyword(s):  
Rice Husk ◽  
Investment Casting ◽  
Open Porosity ◽  
Casting Process ◽  
Casting Defects ◽  
Ceramic Shell ◽  
Volatile Elements ◽  
Shell System ◽  
Mould Filling ◽  
Shell Mould

Basically, permeability of ceramic shell mould system play an important role in minimizing the casting defects in most investment casting shell. The mould has to be sufficiently permeable to obtain complete mould filling during casting process. Mould fill can be improved by increasing the open porosity that definitely will increase permeability ceramic shell mould. The elimination of rice husk volatile elements has contributed to the increment of pore structure that provides a great deal of connected pathways through the ceramic shell which directly will increase the permeability of the ceramic shell mould during casting process. Indeed, the rice husk fibers additions increase the permeability after firing by a factor 3 compared to the standard shell mould system (without fiber) that makes its an excellent alternative in producing higher permeable ceramic shell system.

Vacuum Induction Melting and Investment Casting Technologies Tailored to Near-Gamma TiAl Alloys

2007 ◽  
Vol 539-543 ◽  
pp. 1463-1468 ◽  
Author(s):  
Antonín Dlouhý ◽  
Kateřina Dočekalová ◽  
Ladislav Zemčík
Keyword(s):  
Investment Casting ◽  
Cost Effective ◽  
Melting Process ◽  
Vacuum Induction Melting ◽  
Crucible Wall ◽  
Induction Melting ◽  
Ceramic Shell ◽  
Shell Mould ◽  
Stress States ◽  
As Stress

The present study focuses on vacuum induction melting and investment casting of neargamma TiAl intermetallic alloys. The attention is mainly given to a cost-effective melting process in which a primary alloy ingot is re-melted in a ceramic crucible and cast into a ceramic shell mould. Two types of crucibles (based on Al2O3 and Y2O3) are considered. The most detrimental reactions that govern the contamination of the molten alloy with ceramic particles were determined. Results suggest that the crucible wall attack can be considerably limited by using either the Y2O3 (with no SiO2-type binder) or Al2O3 crucibles with a suitable coating. After pouring, a mechanical interaction associated with different thermal expansions of TiAl casts and ceramic shell moulds can result in serious product damage. A simple 1D-1D model of the cooling process was formulated and the heat flow as well as stress states in the cast-mould system were numerically solved. Process parameters (melt superheat, initial mould temperature, cooling kinetics and mould composition) were optimized in order to reduce the stress in the casts. The optimized parameters delimited a processing window in which complex-shaped TiAl castings like turbocharger wheels can be fabricated.

3D temperature mapping of a ceramic shell mould in investment casting process via infrared thermography

2019 ◽  
Vol 17 (1) ◽  
pp. 40-62
Author(s):  
Carlo Salvatore Greco ◽  
Gerardo Paolillo ◽  
Mattia Contino ◽  
Ciro Caramiello ◽  
Michele Di Foggia ◽  
...  
Keyword(s):  
Infrared Thermography ◽  
Investment Casting ◽  
Casting Process ◽  
Ceramic Shell ◽  
Temperature Mapping ◽  
Shell Mould ◽  
Investment Casting Process

Shell Mould Composite with Rice Husk

2011 ◽  
Vol 471-472 ◽  
pp. 922-927 ◽  
Author(s):  
Z. Harun ◽  
N.H. Kamarudin ◽  
Nur Azam Badarulzaman ◽  
M.S. Wahab
Keyword(s):  
Rice Husk ◽  
Investment Casting ◽  
Strengthening Mechanism ◽  
Green Body ◽  
Ceramic Shell ◽  
Testing Procedures ◽  
The Matrix ◽  
Shell Mould ◽  
Casting Industry ◽  
Reinforced Shell

For many years, precision investment casting foundries have periodically reported serious casting defects. One source is associated with the brittle ceramic shell mould which is very weak in tension and highly expose to the cracking mechanism. This situation not only lead to the appearance of defect in the end cast product but always attribute to the handling problem at the earlier stage in the investment casting industry. Due to this fact the strengthening mechanism of the brittle shell mold using reinforcement method was studied and investigated in this work. Rice husk was chosen as a reinforcement material as it contains silica element which can withstand high temperature of molten metal. Several testing procedures and characterization technique were carried out in order to measure the performance of the reinforced shell mould. Results show that the MOR value for the green reinforced shell mould is higher than the green body of non reinforced shell mould. Scanning electron microscope observations also show that the fiber alignment across the matrix structure increase the failure resistance and yet increase the strength of the shell mould green body. Furthermore, this reinforcement method using organic fiber leads to the pore enhancement and also leads to the new phase formation (zircon) in the fired reinforced body. Overall, this reinforcement method using rice husk increase the properties of the green and fired body of ceramic shell mould system.

The influence of face coat material on reactivity and fluidity of the Ti6Al4V and TiAl alloys during investment casting

2017 ◽  
Vol 231 (1-2) ◽  
pp. 38-48
Author(s):  
Rui L Neto ◽  
Teresa P Duarte ◽  
Jorge L Alves ◽  
Tiago G Barrigana
Keyword(s):  
Investment Casting ◽  
Cast Alloy ◽  
Microstructural Analysis ◽  
Test Sample ◽  
Standard Test ◽  
Tial Alloys ◽  
Alpha Case ◽  
Brittle Layer ◽  
Alternative Materials ◽  
Face Coat

Ti6Al4V alloy belongs to the most significant alloys within the conventional titanium alloys, namely for producing turbochargers impellers and human prostheses. TiAl alloys, because of its attractive properties, such as half density of any nickel-based alloys and excellent high temperature properties, exhibit excellent potential for aerospace turbines and turbocharger turbines application. Investment casting is a near net shape process with great interest for these kind of complex parts, but the processing of these alloys using this technique is still a challenge. In spite of these advantages, these alloys are highly reactive in their molten state, reacting with the ceramic shells used in investment casting, forming a hardened and brittle layer called alpha case on the cast alloy surface, rich in interstitial elements such as oxygen. It is commonly accepted that yttria-based face coats are the best solution for minimizing metal mold reaction, but this ceramic oxide is very expensive. So, the aim of this work is to test alternative materials to produce ceramic shells face coats. A test sample simulating both compressor wheels and turbines was developed and assembled in a wax tree for alpha case and fluidity evaluation. Reactivity studies were conducted based on microhardness measurements and microstructural analysis of γ-TiAl and Ti6Al4V standard test samples, casted in shells with different face coat materials: fused Y2O3, ZrSiO4, Al2O3, yttria (6%) stabilized ZrO2 and yttria stabilized ZrO2 with 10% fine Y2O3 (3–7 µm). The results obtained showed that fused Y2O3 face coat eliminates the alpha case, although affecting the fluidity, and γ-TiAl castings have more misruns blades than Ti6Al4V castings.

Reinforced Green Ceramic Shell Mould for Investment Casting Process

2015 ◽  
Vol 1087 ◽  
pp. 415-419 ◽  
Author(s):  
Zawati Harun ◽  
Noor Hasliza Kamarudin ◽  
Mustaffa Ibrahim ◽  
Maizlinda Izwana Idris ◽  
Sufizar Ahmad
Keyword(s):  
Investment Casting ◽  
Ceramic Body ◽  
Casting Process ◽  
Propagation Mechanism ◽  
Ceramic Shell ◽  
Fibre Bridging ◽  
Pull Out ◽  
Shell Matrix ◽  
Shell Mould ◽  
Investment Casting Process

The development of thin ceramic shell mould in investment casting process is very crucial as this mould inherited brittle property and highly exposed to the cracking mechanism. The slurry composition produces green (unfired) ceramic shell mould which low in strength and easily crack or fail during wax removal or handling process. By strengthening of this brittle ceramic shell mould via reinforcement technique can enhance the strength of green shell mould body. In this work, the presence of the treated rice husk fibre have toughened the green shell mould by creating mechanical interlocking bonding in shell matrix which contributes to higher modulus rupture value. In fact, SEM observations showed that the addition of fiber to the ceramic body to form a composite shell mould prevent the crack propagation mechanism due to the existence of the matrix-fibre bridging which create the resistance of fiber to pull-out. This directly will increase the strength of green shell mould body. .

Effect of Thickness and Permeability of Ceramic Shell Mould on In Situ Melted AZ91D Investment Casting

2013 ◽  
Vol 465-466 ◽  
pp. 1087-1092
Author(s):  
Hassan Jafari ◽  
Mohd Hasbullah Idris ◽  
Ali Ourdjini
Keyword(s):  
Surface Quality ◽  
Investment Casting ◽  
Solidification Rate ◽  
Ceramic Shell ◽  
Good Surface ◽  
Melting Technique ◽  
Shell Mould ◽  
Electron Microscopes ◽  
Scanning Electron Microscopes

The influence of ceramic shell mould thickness and permeability on investment casting of AZ91D alloy using in-situ melting technique was investigated. AZ91D granules together with melting flux were charged into two different moulds having different thicknesses and four various permeabilities; then were heated at 650°C in order to be melted. Visual inspection and scanning electron microscopes were used to characterise the surface quality of cast samples. Thermal analysis was employed to further analyse the effect of mould thickness on cooling and solidification behaviour of molten metal. The findings of this research showed that thinner mould provided higher solidification rate, which is believed to favour in-situ melting enhancement. It enabled melting of the granules at the investigated temperature resulted in suppressing mould-metal reaction and producing cast samples with good surface quality. The results also showed that the permeability of shell mould was ineffective in suppressing mould-metal reaction.

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