The thickness effects of titanium castings on the surface reaction layer

In this study, wedge-shaped CP titanium castings and Ti-6Al-7Nb alloy castings were produced by three types of investment. The effects of the castings' thickness on surface reaction layer were investigated by measuring Vickers hardness, observing the microstructure, and analyzing the oxygen concentration. It was found that the thickness of the surface reaction layer was affected by the thickness of the wedge-shaped castings, and that the hardness value near the surface became lower toward the tip of the wedge-shaped CP titanium and Ti-6Al-7Nb alloy castings. The surface reaction layer of the Ti-6Al-7Nb alloy castings was thinner than that of the CP titanium castings.     

不同包埋材料对Ti-6Al-7Nb合金铸件表面反应层影响的实验研究

目的:研究不同包埋材料对Ti-6Al-7Nb合金表面反应层的影响,筛选出适合于临床应用的包埋材料.方法:利用临床现用的氧化镁系、磷酸盐系、氧化锆系包埋材料分组包埋铸造Ti-6Al-7Nb合金试件,肉眼观察其表面光滑度和粘粉情况;扫描电镜和金相显微镜观察反应层形貌及微观结构;能谱分析仪对反应层元素成分进行分析;显微硬度仪测量反应层硬度及厚度.结果:氧化镁系包埋料组试件表面反应最轻微,未见明显反应层,表面O及其它元素含量极少,表面显微硬度值最低.磷酸盐和氧化锆系包埋料组试件表面反应层可见4层结构,为烧结层、氧化层、包埋料浸入层及金属基体层,并且表面烧结层和氧化层内富含O及包埋料中Al、Zr、Si等元素,随深度增加,包埋料浸入层内O元素含量逐渐减少,仍有少量包埋料中元素成分,直至金属基体层内完全消失,其表面显微硬度值较氧化镁系包埋料组试件高.结论:氧化镁系包埋材料比氧化锆系和磷酸盐系包埋材料更适合于Ti-6Al-7Nb合金.     

不同包埋料对铸钛表面反应层结构的影响

目的比较不同包埋材料对铸钛表面反应层结构的影响。方法制作统一规格的有机玻璃板试样,试验组分别用SYMBION TM,TITAN SUPER MILD A,Ti 21 Investment包埋料内包埋,普通磷酸盐包埋料外包埋,对照组用Multi-Vest包埋料包埋,各铸件沿纵轴截断,采用观测金相组织和显微硬度比较各铸件表面反应层。结果各试验组铸件表面污染层厚度均<80μm,与铸钛表面显微硬度的变化相一致。结论本研究选用的3种钛包埋料,应用二次包埋法包埋,可满足临床需要。     

不同包埋材料对铸造纯钛铸件表面硬化层的影响

目的 研究两种不同包埋材料对铸件表面硬化层的影响.方法 用铸造蜡片制作尺寸为20 mm×20 mm×1.5 mm的片状试件共6片,分为2组,实验组采用新型铸钛包埋材料包埋,对照组采用Rematitan:Plus专用铸钛包埋料包埋铸造.铸件处理后用显微硬度仪测试表面硬度,负重200 g持续5 s,测量维氏显微硬度值,比较...     

Titanium casting using commercial phosphate-bonded investments with quick heating method

The purpose of this study was to investigate the possible use of quick heating method for titanium casting using two commercial investments (Rematitan Plus and Tancovest). The resulting characteristics of the investments with the quick heating method were as follows: residual thermal expansion at the casting temperature was in the range of 0.39 to 0.64%; green strength and fired strength ranged from 4.4 to 10.3 MPa and from 13.8 to 17.6 MPa, respectively. Five full crown titanium castings from each casting condition were obtained using an argon arc melting and gas pressure casting machine. The thickness of cast surface reaction layer was approximately 200 microm, regardless of heating methods or investments. Further, the heating method did not significantly influence either the accuracy or surface roughness of the titanium castings. These results therefore suggested that these commercial investments for titanium could be used for the quick heating method.     

铸模温度对铸钛机械性能及表面反应层结构的影响

钛在高温状态下化学性能活泼，易氧化且与包埋料发生化学反应。我们采用拉伸试验及现代表面分析技术，研究了不同铸模温度对铸钛机械性能及表面反应层结构的影响。结果表明，随着铸模温度升高，铸钛件的抗拉强度、屈服强度增加而延伸率下降，同时，铸钛表面硬化层增厚。用室温铸模铸造时钛铸件表面硬化层厚５０μｍ，用８５０℃铸模铸造时钛铸件表面硬化层厚１２５μｍ。ＳＸｍａｃｒｏ电子探针微区成分分析显示，锆、铝二元素在钛铸件表面扩散深度不随铸模温度增高而加深，但硅元素的扩散则随铸模温度升高而加深。室温铸造时硅元素的扩散深度为３０μｍ，８５０℃铸造时已达９０μｍ。研究结果提示，临床制作铸钛修复体时，必须考虑铸模温度对铸件质量的影响。     

低弹性模量钛铌锆锡合金铸件表面反应层结构的研究

目的:观察铸模温度对钛铌锆锡(Ti-Nb-Zr-Sn)合金铸件表面反应层结构的影响。方法:在两种铸模温度下(室温,300°C)进行合金的铸造。对铸件表面反应层的结构及显微硬度进行测试;采用SEM下的能谱分析(EDS)对铸件抛光前后的表面元素成份进行对比研究。结果:随着铸模温度的提高,Ti-Nb-Zr-Sn合金铸件表面反应层的厚度增加,表面硬度值增大。组织金相显示铸件表面反应层结构可分为3层。铸件表面抛光前元素Si、A1含量较高,抛光后则明显减少。且随着铸模温度的提高,Si的扩散深度及渗透量均有所增加。结论:为了减少Ti-Nb-Zr-Sn合金铸件表面反应层的厚度,应尽量降低铸模温度,同时应选择无Si的包埋材料。     

压差式铸钛机的熔铸条件对纯钛铸件组织结构的影响

目的：分析进口压差式铸钛机铸造的纯钛铸件内部组织结构和缺陷原因，探讨提高纯钛铸造修复体组织结构致密度，减少杂质，避免内部缺陷的方法。方法：应用X－线金属探伤仪定位，数字式金相显微镜分析纯钛铸件内部的组织结构。并应用痕量气体分析仪对气泡内残留成分进行分析，同时对气泡内壁的组织结构进行金相学分析。结果：纯钛铸件内部的气泡主要来自于熔铸室的氩气保护和铸道直径过细，过长所致。结论：短、粗铸道和改进熔铸室的氩气保护方式是减少铸件内部缺陷的关键。     

Dimensional accuracy analysis of implant framework castings from 2 casting systems

PURPOSE: To compare the dimensional accuracy of implant framework castings from an argon vacuum casting machine with those from a centrifugal casting machine. MATERIALS AND METHODS: Three 4 x 10-mm external hex-type implants (3i/Implant Innovations) were embedded in an acrylic resin block 7 mm apart, with a 2 mm offset of the middle implant. Eight reference points were marked on the implant collars. Twenty implant bar frameworks were waxed with UCLA abutments, invested with a ringless system, and subjected to the same thermal cycle. Ten wax patterns were cast in gold alloy using an oxygen-propane torch and centrifugal casting system; 10 were cast using an argon vacuum casting machine (KDF; Denken). The White 1-screw technique was applied after sequentially tightening the mesial and distal abutment screws to 10 Ncm. Fit of the implant framework castings was evaluated by measuring the marginal opening between the casting and implant at the reference points. These measurements were averaged and statistically compared for differences. RESULTS: The mean marginal openings at the most distant measuring locations from the tightened retaining screw at location 1 was between 44 to 48 microm for the centrifugal system compared to between 28 to 32 mm for KDF (P < .01). For screws tightened at location 3, the mean marginal openings at the most distant measuring locations were between 40 to 51 mm for the centrifugal system compared to between 27 to 29 microm for KDF (P < .01). DISCUSSION: In comparison with the centrifugal casting and oxygen-propane system, the argon vacuum system was more accurate and user friendly and less technique-sensitive. CONCLUSION: The argon vacuum casting machine tested produced more accurate, better fitting implant-supported prosthesis frameworks than a conventional centrifugal casting system. The "1-screw" method of evaluating casting fit was most effective when either of the prostheses' end screws were tightened.     

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 microm 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 microm. 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.     

The fit of gold-alloy full-crown castings made with pre-wetted casting ring liners.

Measurements were made of the fit of full-crown gold-alloy castings produced with two types of pre-wetted ring liner (asbestos and cellulose) and a typical gypsum-bonded investment (Cristobalite Inlay, Sybron/Kerr Products, Romulus, MI; W/P = 0.40). Laboratory measurements were made of the effects of the liners on potential investment expansion, and properties of the lining materials considered relevant to casting accuracy were also measured. There was a wide variation in values for mean dimensional inaccuracy. One liner produced a series of castings all of whose inaccuracies lay within the range +/- 0.1%, with a mean value of + 0.01%. With the other five liners, all or most castings were undersize. With three, all or most castings showed inaccuracies worse than -0.2%. The values for casting inaccuracy with the various liners showed a probable correlation with potential investment expansion (p < 0.05); however, no correlation was found between casting inaccuracy and any apparently relevant liner properties, alone or in combination. In casting techniques which use a pre-wetted ring liner, the choice of a specific lining material is an important factor which has a significant effect on casting inaccuracy. With at least three of the six liners tested, a higher investment expansion was needed for accurate full-crown castings to be ensured.