Titanium Investment Research Articles

Neutron radiography inspection of investment castings

Investment casting, also known as the lost wax process, is a manufacturing method employed to produce near net shape metal articles. Traditionally, investment casting has been used to produce structural titanium castings for aero-engine applications with wall thickness less than 1 in (2.54 cm). Recently, airframe manufacturers have been exploring the use of titanium investment casting to replace components traditionally produced from forgings. Use of titanium investment castings for these applications reduces weight, cost, lead time, and part count. Recently, the investment casting process has been selected to produce fracture critical structural titanium airframe components. These airframe components have pushed the traditional inspection techniques to their physical limits due to cross sections on the order of 3 in (7.6 cm). To overcome these inspection limitations, a process incorporating neutron radiography (n-ray) has been developed. In this process, the facecoat of the investment casting mold material contains a cocalcined mixture of yttrium oxide and gadolinium oxide. The presence of the gadolinium oxide, allows for neutron radiographic imaging (and eventual removal and repair) of mold facecoat inclusions that remain within these thick cross sectional castings. Probability of detection (POD) studies have shown a 3× improvement of detecting a 0.050×0.007 in 2 (1.270×0.178 mm 2) inclusion of this cocalcined material using n-ray techniques when compared to the POD using traditional X-ray techniques. Further, it has been shown that this n-ray compatible mold facecoat material produces titanium castings of equal metallurgical quality when compared to the traditional materials. Since investment castings can be very large and heavy, the neutron radiography facilities at the University of California, Davis McClellan Nuclear Radiation Center (UCD/MNRC) were used to develop the inspection techniques. The UCD/MNRC has very unique facilities that can handle large parts up to 39 ft (12 m) in length and 13 ft (4 m) high weighing up to 5000 lbs (2300 kg). These handling systems are robotically driven. The neutron radiographic system consists of a highly thermalized neutron beam. The neutron beam has an intensity of 5.6×10 6 n/cm 2 s, with a L/ D=200 at a power of 2 MW. A divergent beam collimator is used which provides a beam of approximately 22 in (56 cm) in diameter at the film plane. A vacuum cassette with a gadolinium vapor deposited screen is used to collect the image. Exposure times can be as short as 3 min, or up to 30 min.

Modeling the surface contamination of dental titanium investment castings

Objective: The objective of this study was to develop a computational tool for assisting the design of titanium dental castings with minimal defects and to compare computational simulations with casting experiments. Methods: Modeling. An in-house cellular-automata solidification and finite-difference diffusion program was coupled with a commercial casting program and applied to (a) simple geometric wedge models and (b) a 3D-laser scan of a molar crown casting. Experimental. Wedges and molar crowns were hand-waxed and investment cast in commercial purity grade 1 (CP-1) titanium by a commercial dental laboratory. The castings were sectioned and analyzed using light and scanning electron microscopy, X-ray microanalysis, and microhardness testing. Results: In the wedge sample, contamination with impurities (Al, Si), including intermetallic precipitates, was found to extend to a depth ranging from 30 to 120 μm depending on the section thickness and hence the local cooling rate. Microstructural and mechanical (hardness) effects were found to a depth ranging from 80 to 250 μm. The coupled micro/macro model predictions showed reasonable agreement for the pattern of contamination. Significance: Dental and medical applications demand close dimensional tolerance and freedom from surface impurities and structural flaws in castings having unique shapes. The ability to predict the structural, mechanical, and chemical changes resulting from the casting process will help to design the casting and post-casting processes to minimize these problems.

Phosphate-bonded ZrSi04 Investments Added with ZrC and ZrN for Casting Titanium

In this study, new investments for titanium were developed by adding ZrC or ZrN as chemical additive for thermal expansion to a phosphate-bonded zircon (ZrSiO4) investment. The following effects were then examined: setting expansion, residual thermal expansion, and compressive strength of these experimental investments; surface roughness of cast plate; and casting accuracy of titanium crown. For residual thermal expansion, it occurred even while investments were cooled to room temperature after firing in air atmosphere. This was due to the additives' oxidation to ZrO2--suggesting that residual thermal expansion increased with increased amount of these additives. As for casting accuracy of full-crown cast into molds at room temperature, it correlated with the ZrN content. Hence by adding the right amount of ZrN, cast titanium crowns with low surface roughness and good adaptability could be obtained.

チタン専用埋没材の諸性質と鋳造冠内面の形状変化

In order to clarify the properties of investments for titanium and the inner surface form change of a cast crown, a survey of roughness, hardness (Hv), compressive strength, setting expansion, and thermal expansion was made by using five kinds of titanium investment as well as by changing the condition of heating or not heating. Three kinds of investment except alumina having a very rough surface were selected, and cast crowns were made by changing the condition of using or not using the relief. The inner surface form change was comparativery investigated by a three-dimensional measurement system. The result were as follows:1. As for setting expansion, the materials were divided into three types, i.e., the first was Selevest, Titavest, and Titanmold which remained fixed for two hours, the second was Titanium which indicated 0.2% at twenty minutes, and the last was Ceravest whose setting expansion increased from the beginning indicating 1.2% at ninety minutes.2. As for thermal expansion, Selevest, Titavest, and Titanmold contracted by heating but Ceravest and Titanium expanded.3. The indicated heating expansion rates were 0.2% for Selevest at 200°C, 0.6% for Titavest at 600°C, 0.5% for Ceravest and 0.5% for Titanium at normal temperature, and 0.3% for Titanmold at 800°C.

Development of Yttria-based Investments for Titanium Casting

Development of Yttria-based Investments for Titanium Casting