Grindability of alpha-case formed on cast titanium.

The hardened alpha-case (alpha-case) layer inevitably forms on the surface of titanium castings when prepared by investment casting. Because the hardness of the alpha-case is incomparable to that of the interior structure, the perception exists that the alpha-case is difficult to remove during cutting, grinding and polishing. Grindability (ease of grinding) of cast cpTi and cast Ti-6Al-4V was evaluated by grinding cast specimens incrementally using a SiC abrasive wheel. The present study revealed that the presence of the brittle alpha-case with lower fracture toughness is beneficial in grinding titanium. The alpha-case on the ductile cpTi can be ground much easier than its bulk interior structure. In less ductile Ti-6Al-4V, the grinding rate is much higher than that of cpTi, and the alpha-case and its interior structure are at similar levels since the fracture toughness of its alpha-case and the bulk material is not large enough.

Ion release from casts of commercially pure titanium in mixed solutions of organic acids contained in human saliva.

PURPOSE: The purpose of this study was to investigate the ion release from titanium casts in solutions of mixed organic acids and to reconsider the possibility of allergic reactions to titanium. METHODS: Cast specimens were made from commercially pure titanium. For the immersion solutions, we prepared two types of organic acid solutions, one mixed with organic acids contained in whole stimulated saliva at two different dilutions, and the other, a lactic acid solution. Following immersion, the amounts of dissolved titanium ions, weight loss of the casts, and micrographs of the specimen surfaces were examined. RESULTS: There were significantly larger amounts of dissolved titanium ions in the mixed organic acid solutions than in the lactic acid solution. There was also a significant difference in the weight loss values between the immersion solutions (p < 0.0001), but the significance level was different from that of the difference in the quantity of ion elution. CONCLUSION: The results suggested that a much larger quantity of ions is released from titanium casts attached in the oral cavity than has been reported previously, and that it is necessary to consider the possibility of allergic reactions to titanium casts.

Modeling wear of cast Ti alloys.

The wear behavior of Ti-based alloys was analyzed by considering the elastic-plastic fracture of individual alloys in response to the relevant contact stress field. Using the contact stresses as the process driving force, wear was computed as the wear rate or volume loss as a function of hardness and tensile ductility for Ti-based cast alloys containing an alpha, alpha+beta or beta microstructure with or without the intermetallic precipitates. Model predictions indicated that wear of Ti alloys increases with increasing hardness but with decreasing fracture toughness or tensile ductility. The theoretical results are compared with experimental data to elucidate the roles of microstructure in wear and contrasted against those in grindability.

[A case of burning mouth associated with dental metal allergy].

PATIENT: A 70-year-old male presented with a history or chief complaint of burning and prickly sensation in the oral cavity at two years after dental treatments. We diagnosed that this symptom might be due to hypersensitivity reaction to the Zn, Co and Hg used in dental prostheses based on the results of patch testing and metal analysis. After removal of all the suspected metals, the symptom disappeared. DISCUSSION: Many alternative causes have been proposed for burning mouth. As reported previously, mucosal allergic reactions have developed into burning mouth in patients. It is advisable to perform patch tests in selected patients to identify a possible etiological agent. Although patch testing for these symptoms might provide useful information, it is difficult to characterize the significance of contact allergy. Therefore, careful diagnosis, treatment and follow-up are necessary alleviate to symptoms of such case. CONCLUSION: This case showed that metal allergy might be related to the condition of burning mouth.

Corrosion behavior of cast Ti-6Al-4V alloyed with Cu.

It has recently been found that alloying with copper improved the inherently poor grindability and wear resistance of titanium. This study characterized the corrosion behavior of cast Ti-6Al-4V alloyed with copper. Alloys (0.9 or 3.5 mass % Cu) were cast with the use of a magnesia-based investment in a centrifugal casting machine. Three specimen surfaces were tested: ground, sandblasted, and as cast. Commercially pure titanium and Ti-6Al-4V served as controls. Open-circuit potential measurement, linear polarization, and potentiodynamic cathodic polarization were performed in aerated (air + 10% CO(2)) modified Tani-Zucchi synthetic saliva at 37 degrees C. Potentiodynamic anodic polarization was conducted in the same medium deaerated by N(2) + 10% CO(2). Polarization resistance (R(p)), Tafel slopes, and corrosion current density (I(corr)) were determined. A passive region occurred for the alloy specimens with ground and sandblasted surfaces, as for CP Ti. However, no passivation was observed on the as-cast alloys or on CP Ti. There were significant differences among all metals tested for R(p) and I(corr) and significantly higher R(p) and lower I(corr) values for CP Ti compared to Ti-6Al-4V or the alloys with Cu. Alloying up to 3.5 mass % Cu to Ti-6Al-4V did not change the corrosion behavior. Specimens with ground or sandblasted surfaces were superior to specimens with as-cast surfaces.

Evaluation of the amalgamation reaction of experimental Ag-Sn-Cu alloys containing Pd using a mercury plating technique.

A mercury plating technique was used to determine the phases forming on experimental Ag-Sn-Cu alloy powders (with and without Pd) exposed to electrolytically deposited mercury. Four series of alloy powders were made: a) 1.5% Pd with 10-14% Cu (CU series); b) 1.0% Pd with 10-14% Cu (1PD series); c) 1.5% Pd with different ratios of Ag3Sn (gamma) to Ag4Sn (beta) with 12% Cu (AGSN series); and d) 9-13% Cu with no Pd (NOPD series). Each powder was pressed on a freshly prepared amalgam specimen made from the same powder and metallographically polished until cross sections appeared; mercury was electroplated on the alloy particles. Alloy powders, amalgams and electroplated specimens were examined using XRD and SEM/EDS. XRD confirmed the presence of gamma2 in amalgams made from alloys with Cu < 13% or with Ag3Sn/Ag4Sn > 0.8. Specimens with moderately plated Hg showed gamma1 (Ag2Hg3) polyhedra and eta' Cu6Sn5, but not gamma2. This method effectively identifies alloys prone to forming gamma2.