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PubMedDate not supplied

Surface characterizations of variously treated titanium materials.

The attachment of cells to titanium surfaces is an important phenomenon in the area of clinical implant dentistry. A major consideration in designing implants has been to produce surfaces that promote desirable responses in the cells and tissues. To achieve these requirements, the titanium implant surface can be modified in various ways. This research was designed to elucidate the relationship between surface roughness (Ra) and contact angle (theta) of various engineered titanium surfaces of commercially pure titanium, titanium-aluminum-vanadium alloy (Ti-6Al-4V), and titanium-nickel (TiNi) alloy. The contact angle was measured using distilled water, 1% sodium chloride solution, human neutrophils, and osteoblast-like cells. Surface oxide crystallography was identified by transmission electron diffraction. It was found that: (1) there were no significant differences in contact angles among the 4 media; (2) for commercially pure titanium, a combined treatment (hydrofluoric acid/nitric acid/water --> sodium hydroxide --> oxidation) showed the lowest theta (10.51 degrees in water), while the surface treated with sulfuric acid showed the highest value (72.99 degrees in water); (3) for all commercially pure titanium samples, when theta is greater than 45 degrees, the contact angle increases linearly with Ra (hydrophobic nature) and the surface is covered with rutile-type oxide only, while the contact angle decreases linearly with Ra when theta is less than 45 degrees (hydrophilic nature) and the surface is covered with a mixture of rutile and anatase oxides; and (4) a similar trend was found on Ti-6Al-4V and TiNi surfaces.

Acid Etching, Dental↗

PubMedDate not supplied

Comparison of load distribution for implant overdenture attachments.

PURPOSE: The aim of this study was to compare the force and moment distributions that develop on different implant overdenture attachments when vertical compressive forces are applied to an implant-retained overdenture. MATERIALS AND METHODS: The following attachments were examined: Nobel Biocare bar and clip (NBC), Nobel Biocare standard ball (NSB), Nobel Biocare 2.25-mm-diameter ball (NB2), Zest Anchor Advanced Generation (ZAAG), Sterngold ERA white (SEW), Sterngold ERA orange (SEO), Compliant Keeper System with titanium shims (CK-Ti), Compliant Keeper System with black nitrile 2SR90 sleeve rings (CK-70), and Compliant Keeper System with clear silicone 2SR90 sleeve rings (CK-90). The attachments were tested using custom strain-gauged abutments and 2 Brånemark System implants placed in a test model. Each attachment type had one part embedded in a denture-like housing and the other part (the abutment) screwed into the implants. Compressive static loads of 100 N were applied (1) bilaterally, over the distal midline (DM); (2) unilaterally, over the right implant (RI); (3) unilaterally, over the left implant (LI); and (4) between implants in the mid-anterior region (MA). Both the force and bending moment on each implant were recorded for each loading location and attachment type. Results were analyzed using 2-way analysis of variance and the Duncan multiple-range test. RESULTS: Both loading location and attachment type were statistically significant factors (P < .05). In general, the force and moment on an implant were greater when the load was applied directly over the implant or at MA. DISCUSSION: While not significant at every loading location, the largest implant forces tended to occur with ZAAG attachments; the smallest were found with the SEW, the SEO, the NSB, the CK-70, and the CK-90. Typically, higher moments existed for NBC and ZAAG, while lower moments existed for SEW, SEO, NSB, CK-90, and CK-70. CONCLUSION: For different loading locations, significant differences were found among the different overdenture attachment systems.

Analysis of Variance↗

PubMed1997

Effects of metal ions on osteoblast-like cell metabolism and differentiation.

The objective of this study was to evaluate the effects of metal ions, which may be released from orthopedic or dental implants, on osteoblast metabolism and differentiation. ROS 17/2.8 cells were cultured in F-12 medium for 7 days. Then Al+3, Co+2, Cr+3, Ni+2, Ti+4, and V+3 were added at concentrations less than their cytotoxic concentrations. After 3 days, DNA synthesis, succinate dehydrogenase activity, alkaline phosphatase (ALP) activity, and culture calcification were assessed. Northern blots were performed for ALP, osteocalcin (OCN), and osteopontin (OPN) mRNA transcription. The data indicated that Cr+3 and A1+3 had few inhibitory effects on ROS cell metabolism below their cytotoxic concentrations, Ni+2, Co+2, Ti+4, and V+3 affected all these parameters of ROS cell metabolism at concentrations below cytotoxic levels. For RNA analysis, A1+3 significantly suppressed the expression of ALP, OCN, and OPN at both cytotoxic and noncytoxic concentrations. Co+2 specifically suppressed ALP expression at cytotoxic concentrations. Cr+3 and Ni+2 inhibited OCN, OPN, and ALP gene expression only at cytotoxic concentrations. For Ti+4 and V+3 ions, gene expression at cytotoxic levels was not significantly affected as compared with the effects at noncytotoxic level. These results show that metal ions may alter osteoblast behavior even at subtoxic concentrations, but do not always affect the expression of all genes similarly.

Blotting, Northern↗

PubMed2006

Nano-structural bioactive gradient coating fabricated by computer controlled plasma-spraying technology.

The poor mechanical property of hydroxyapatite was the major problem for load bearing and implant coating in clinical applications. To overcome this weakness, a bioactive gradient coating with a special design composition of hydroxyapatite (HA), ZrO2, Ti, bioglass was developed. This 120 microm coating with an upper layer of 30-50 microm porous HA produced by computer controlled plasma spraying which maintained energy level of the plasma which ensure proper melting of powder. The crystal size of the coating was 18.6-26.2 nm. Transformation of t-ZrO2 to m-ZrO2 reduced the thermal stress that weakened the coating and lowered down interfacial strength of the coating and metal substrate. Thermal stress of sprayed coating was 16.4 MPa which was much smaller than the sample without thermal treatment of 67.1 MPa. Interfacial strength between the coating and metal substrate was 53 MPa which is much higher than conventional Hydroxyapatite coating. Based on XRD analysis crystallinity of HA approached 98%. Therefore, high temperature treatment improved long term stability of the coating through improved crystallinity of hydroxyapatite and reduced other impure calcium phosphate phase.

Aluminum Oxide↗

PubMed2002

An in vitro investigation of plasma sprayed hydroxyapatite (HA) coatings produced with flame-spheroidized feedstock.

The in vitro behaviour and characteristics of plasma sprayed hydroxyapatite (HA) coatings using flame-spheroidized HA feedstock powder on titanium alloy (Ti-6Al-4V) substrates were investigated in a simulated physiological environment as an attempt to reflect the actual incubational condition of an implant in a human body system. As-sprayed and heat-treated HA coatings were immersed in a simulated body fluid with ionic concentrations comparable to that of human blood plasma for time intervals 2, 4, 6, 8 and 10 weeks. Rapid dissolution of calcium phosphate was found to occur within the first 4 weeks, and after the 5th week a retarding rate of 4.1 mM week(-1) was observed where precipitation, nucleation, and, growth of a carbonate-containing, poorly crystallized or amorphous calcium phosphate layer on the as-sprayed coatings were noted. The heat-treated coatings showed minimal or no precipitation on the surface except for the presence of calcite minerals that is due to carbonation effect. Complete dissolution of other calcium phosphate phases such as tetracalcium phosphate, tricalcium phosphate and calcium oxide was also noted after 2 weeks of immersion due to higher ionic solubility relative to HA. A declining trend in respective microhardness and elastic modulus of the as-sprayed HA coatings from 207.06 +/- 3.2 H(k300) to 131.8 +/- 5.2 H(k300) and from 31.37 +/- 1.4 to 19.81 +/- 1.6 GPa was observed after 10 weeks of immersion. Tensile bond strength of both types of coatings showed similar declining trend, with an average dip from 24.5 +/- 2.4 to 7.9 +/- 2.6 MPa. Nevertheless. the heat-treated samples showed rather reasonable mechanical stability and structural integrity of 26.7 +/-1.4 GPa in elastic modulus after soaking.

Alloys↗

PubMed1999

An in vitro model for mineralization of human osteoblast-like cells on implant materials.

An in vitro mineralizing cell-implant system was developed to study osteoblast attachment, secretion of extracellular (ECM) matrix proteins and mineralization. Saos-2 cells were plated on Tivanium (Tiv, Ti-6A1-4V), Zimaloy (Zim, Co-Cr-Mo) and glass disks. The cells were cultured in alpha-MEM medium with 10% fetal bovine serum and 50 microg ml(-1) ascorbic acid. The cultures were analyzed for calcification and for mRNA expression for ECM proteins after 1, 2, 4 and 6 weeks. Calcium content was significantly higher in cells on Tiv, less on Zim and least on glass disks. With the addition of 3 mm beta-glycerophosphate (beta-GP), the cell layer was more calcified on Zim than on Tiv and all substrates had three times more calcium than cultures without beta-GP. All subsequent experiments were performed without beta-GP. Phalloidin immunofluorescence microscopy of the actin-based cytoskeleton at 2 weeks demonstrated nodules composed of multilayered, cobblestone-appearing osteoblasts overlying calcified matrix which was stained with calcein. On Tiv, calcified nodules were connected in a trabecular-like pattern while on Zim, calcification was dispersed throughout the cell layer. Northern blots for alkaline phosphatase, bone sialoprotein, osteocalcin and alpha1(I) procollagen mRNAs were performed at different time points. The amount and pattern of calcification as well as the expression of ECM-mRNAs differed on each implant material. The results indicate that Tiv stimulates the production of more ECM proteins and mineralized matrix than Zim or glass in this osteoblast-like cell/implant culture.

Alloys↗

PubMed2005

Effects of hydrogen peroxide solutions on artificial hip joint implants.

This study was designed to elucidate the erosive effect of hydrogen peroxide solutions on the materials used for total-hip arthroplasty (THA). As test materials, cross-linked polyethylene, Ti-6Al-4V alloy, and thermal sprayed hydroxyapatite (HA) were used. Changes upon soaking in 3% hydrogen peroxide, before soaking, 1 minute after soaking, 10 minutes after soaking, and 180 minutes after soaking were examined. Scanning electron microscope, Fourier transform infrared analysis, and x-ray diffraction were used for this examination. Hydrogen peroxide did not affect polyethylene, although notable changes in the Ti-6Al-4V alloy and HA did occur. These results indicate that caution should also be exercised to minimize erosion of prosthesis consisting of HA and Ti alloy when hydrogen peroxide solutions are used during total-hip arthroplasty.

Alloys↗

PubMed2002

An experimental study of the dissemination of Titanium and Zirconium in the body.

Metallic implants can generate and release titanium oxide (TiO(2)) and zirconium oxide (ZrO(2)) to the tissues. These products can accumulate locally or disseminate systemically. The aim of the present study was to assess the distribution of TiO(2) and ZrO(2) administered intraperitoneally to rats. We used male Wistar rats of approximately 100 g body weight throughout the study. An intraperitoneal injection of a suspension of TiO(2) or ZrO(2) (16, 1600 and 16 x 10(3) mg/kg body weight) was administered. The animals were killed at 5-10 months post-administration by ether overdose. Samples of peritoneum, liver, kidney, lung and spleen were taken, fixed in formalin and routine processed for embedding in paraffin. One set of sections was stained with hematoxylin and eosin and another set was prepared unstained. The presence of titanium in the tissues was detected by X-ray diffraction crystallography. The histological analysis revealed the presence of abundant intracellular aggregates of metallic particles of Ti and Zr in peritoneum, liver, lung and spleen. The crystallographic study revealed the presence of anatasa. The dissemination of metallic particles from orthopedic or odontological implants would not be restricted to a local phenomenon. The particles also target vital organs. The distribution of these deposits over lengthy periods deserves meticulous attention given the clinical relevance of this phenomenon.

Journal Article↗

PubMedDate not supplied

[Standardized testing of bone implant surfaces with an osteoblast cell culture system. II. Titanium surfaces of different degrees of roughness].

The effect of titanium surfaces with different degrees of roughness on osteoblast proliferation and differentiation was investigated using a standardised cell culture system. Human foetal osteoblasts (hFOB 1.19) were cultured on polished (Ti pol), sandblasted (Ti sb) and sandblasted/heat treated (Ti sb-ht) titanium surfaces for 17 days. Cell culture quality polystyrene (Ps) was used as a control. Cell number and viability were determined for assessment of proliferation. Alkaline phosphatase activity, collagen I and osteocalcin production were measured as parameters for osteoblast differentiation. In the early phase, higher proliferation values were measured on Ti pol. However, on Ti sb and Ti sb-ht higher proliferation was found in the late phase. The activity of the early differentiation marker alkaline phosphatase was higher on Ti pol. No differences were seen for the late differentiation parameters collagen I and osteocalcin. The test system permits the influence of the surface structure on the dynamics of the osteoblast development cycle to be determined. The larger surface area of rough materials leads to an initially delayed, but then prolonged cell proliferation. This model correlates with recent in vivo findings, and confirms the use of rough surfaces for implants in direct contact with bone, even at the cellular level.

Cell Differentiation↗

PubMed2006

Oxygen plasma surface modification enhances immobilization of simvastatin acid.

Simvastatin acid (SVA) has been reported to stimulate bone formation with increased expression of BMP-2. Therefore, immobilization of SVA onto dental implants is expected to promote osteogenesis at the bone tissue/implant interface. The aim of this study was to evaluate the immobilization behavior of SVA onto titanium (Ti), O(2)-plasma treated titanium (Ti + O(2)), thin-film coatings of hexamethyldisiloxane (HMDSO), and O(2)-plasma treated HMDSO (HMDSO + O(2)) by using the quartz crystal microbalance-dissipation (QCM-D) technique. HMDSO surfaces were activated by the introduction of an OH group and/or O(2)-functional groups by O(2)-plasma treatment. In contrast, titanium surfaces showed no appreciable compositional changes by O(2)-plasma treatment. The QCM-D technique enabled evaluation even at the adsorption behavior of a substance with a low molecular weight such as simvastatin. The largest amount of SVA was adsorbed on O(2)-plasma treated HMDSO surfaces compared to untreated titanium, HMDSO-coated titanium, and O(2)-plasma treated titanium. These findings suggested that the adsorption of SVA was enhanced on more hydrophilic surfaces concomitant with the presence of an OH group and/or O(2)-functional group resulting from the O(2)-plasma treatment, and that an organic film of HMDSO followed by O(2)-plasma treatment is a promising method for the adsorption of SVA in dental implant systems.

Adsorption↗

PubMed1993

[Biodeterioration and corrosion of metallic implants and prostheses].

The use of surgical implants and prosthetic devices to replace the original function of different components of the human biological system is a well established tradition in the history of medicine. Currently, one of the most prevalent points of view in dealing with this subject, is that of biocompatibility of materials of construction and methods of fabrication of these devices, in order to avoid negative impacts on the patient due to failure of implants through degradation mechanisms such as corrosion. This article presents a current general review of the relationship between biocompatibility and deterioration of metallic implants and prosthetic devices, emphasizing the specific forms that corrosion adopts in biological media. The historical perspective shows the consolidation of a tendency towards a more systematic study of these phenomena in recent years, as opposed to trial and error practices that used to be common before the third decade of this century. The understanding of interactions between implants and biological tissue, thus led to some of the most promising current techniques, such as the use of powder metallurgy components to optimize skeletal fixation of implants by means of interstitial bone growth into porous metallic surfaces. The review of metals and alloys currently used for the fabrication of implants shows the amplitude of available technological alternatives, as well as the multiple criteria required to make a good selection for each specific case. Applications and pros and cons of stainless steel, Cr, Ni, Co and Ti alloys, and tantalum are briefly discussed. The introduction to basic concepts of corrosion, serves as a basis for the description of the typical forms that these phenomena adopt in biological media, including pitting, crevice corrosion, fatigue-corrosion, stress corrosion, fretting corrosion, galvanic corrosion, and intergranular corrosion. This review shows that the study of interactions between biological media and metallic implants has become a well established and specific field of science. As a result of this conclusion, an interdisciplinary treatment of the subject of biodeterioration of metallic implants and prosthetic devices is proposed. In practical terms, this proposal can be understood as the integration of an expert in materials science and engineering to the medical team. Thus, quality and reliability of the implant, as well as maximization of its useful life, would be achieved through the implementation of technical specifications, accepted standards, and pertinent testing as recommended by the above mentioned expert, who will be the person of the team more able to grasp the novelties that the dynamic field of biomaterials constantly offers.

Biocompatible Materials↗

PubMed1998

Calcium phosphate induction by sol-gel-derived titania coatings on titanium substrates in vitro.

Titanium and its alloys are used widely in the manufacture of orthopedic and dental implants. Sol-gel-prepared titania is able to stimulate bone-like apatite formation in in vitro and in vivo cultures. These materials can be used, for example, as coatings on dental and orthopedic implants. However, the processes that lead to apatite formation are not fully understood. In this study different kinds of titania coatings on commercially pure titanium (c.p. Ti) were tested for apatite-forming ability. The rate of apatite formation is considered to be descriptive of a material's bioactive (bone-bonding) potential. Apatite-forming tests were done in simulated body fluid (SBF). Apatite-forming ability was highest with the addition of valeric acid to sol (600 degrees C) or with sintering sol-gel coatings at 450 degrees-550 degrees C. At that temperature range calcium phosphate forms on the coatings in 1 week. Calcium phosphate forming is observed in 1 day on standard coatings sintered at 500 degrees C.

Biocompatible Materials↗

PubMed2000

Re-establishment of the atomic composition and the oxide structure of contaminated titanium surfaces by means of carbon dioxide laser and hydrogen peroxide: an in vitro study.

BACKGROUND: In clinical situations with peri-implant bone resorption, re-integration of the exposed implant surface is sometimes preferable, which requires a clean surface. Previous investigations have shown that cleaning of contaminated titanium surfaces using chemical and abrasive methods is difficult. PURPOSE: The aim of this investigation was to evaluate the efficacy of different combinations of chemical and physical methods (citric acid, hydrogen peroxide, and carbon dioxide [CO2] laser irradiation) for removal of contaminants and subsequent reconstruction of the surface oxide of intraorally contaminated titanium foils. MATERIALS AND METHODS: Commercially pure titanium foils (99.6%, 5 x 5 mm in size) were contaminated by placement on dentures in volunteering patients, simulating a peri-implantitis situation. The contaminated foils and clean control foils were treated by seven and six combinations of citric acid, hydrogen peroxide, and CO2 laser irradiation, respectively. The effect of the cleaning procedures was evaluated by x-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM). RESULTS: The initial elemental composition of the contaminated foils was 70% carbon (C), 20% oxygen (O), 10% nitrogen (N), and only traces of titanium (Ti) (< 1%). One treatment proved to be more effective than the others: irradiations by 5-second cycles of superpulsed CO2 laser at a power of 7 W, 10-millisecond pulse width, and with an 80-Hz frequency on a wet surface, followed by repeated application of supersaturated citric acid for 30 seconds, each time followed by rinsing with ultrapure water until all tissue remnants had been removed. Finally, hydrogen peroxide of 10-mM concentration was added to the implant surface and evaporated by CO2 laser at the same settings. This treatment protocol resulted in 10% Ti, 45% O, 41% C, and 2 to 3% N, a composition comparable to that of unused foils: 9% Ti, 40% O, 48% C, and traces of N and chlorine (CI). X-ray photoelectron spectroscopy profiles showed that the thickness of the surface oxide was restored and even augmented with this protocol for treatment of contaminated titanium. CONCLUSION: A combination of citric acid, hydrogen peroxide, and CO2 laser irradiation seems to be effective for cleaning and reestablishment of the atomic composition and oxide structure of contaminated titanium surfaces.

Carbon↗

PubMed1999

Protein adsorption and osteoblast responses to heat-treated titanium surfaces.

The clinical success of dental implants is governed in part by surface properties of implants and their interactions with the surrounding tissues. The objective of this study was to investigate the effect of heat-treated titanium (Ti) surfaces on protein adsorption and osteoblast responses in vitro. The passivated Ti samples used in this study were either nonheat-treated or heat-treated at 750 degrees C for 90 minutes. Using x-ray diffraction analyses, no oxide peaks were observed on the nonheat-treated surfaces, suggesting an amorphous oxide. Crystalline rutile TiO2 peaks were observed on the heat-treated Ti surfaces. The contact angles of water on heat-treated Ti surfaces (32.0 +/- 2.5 degrees) were statistically lower compared with the nonheat-treated Ti surfaces (47.7 +/- 2.3 degrees). In addition, the mean albumin concentration on the nonheat-treated Ti surfaces (3.57 +/- 0.33 micrograms/mL) was observed to be significantly different from the mean albumin concentration on heat-treated Ti surfaces (2.25 +/- 0.26 micrograms/mL). In the presence of an osteoblast precursor cell line, significantly different hexosaminidase activity, protein production, and alkaline phosphatase activity were observed for cells grown on heat-treated Ti surfaces compared with nonheat-treated Ti surfaces.

Adsorption↗

PubMed2003

[In vitro toxicity and mutagenicity of CoCrMo and TiAl wear particles].

Contact of wear particles with body fluids can result in widespread dissemination of extractable constituents from joint implants. The aim of this in vitro study is to clarify whether there is a mutagenic and/or carcinogenic risk from Co(28)Cr(6)Mo and Ti(6)Al(4)V wear particles. Particles of a representative size were produced by fretting; toxicity and mutagenicity were investigated using the Ames Salmonella/microsome test and the V79-HGPRT Test (Chinese hamster fibroblasts). To obtain the greatest possible elution of all constituents, the metallic wear particles were extracted with DMSO and water and the resulting eluates mixed together. After repeated test series under standardized conditions, neither the bacterial nor the mammalian cell assays produced evidence of toxic or mutagenic effects in the concentration range under study. It is therefore not to be expected that CoCrMo or TiAl alloys initiate carcinogenesis in the human organism.

Alloys↗

PubMed1998

Plasma sprayed hydroxyapatite coatings on titanium substrates. Part 2: optimisation of coating properties.

Heat treatment and the introduction of a Ti bond coat have been applied to hydroxyapatite (HA) coatings sprayed using different plasma powers and gas mixtures. Attempts were made in this way to achieve optimal coating properties for orthopaedic implants. In particular, the effects on the degree of crystallinity, the adhesion, the OH ion content and the purity were evaluated. Heat treatment at 700 C for 1 h in air proved to be effective in increasing the crystallinity, regaining the OH- ion and removing other non-HA compounds, although it caused a significant decrease in the degree of adhesion (interfacial fracture toughness) for those specimens sprayed at high powers. This heat treatment was found to induce significant transformation of amorphous HA to the crystalline form, while not detrimentally changing the properties of the underlying Ti-6Al-4V substrates. Precoating with a 100 microm Ti layer increased the adhesion of the HA coatings on Ti-6Al-4V substrates, primarily by providing a rougher surface and promoting better mechanical interlocking. Changes in coating properties during immersion in biological fluids were also studied and were found to depend critically on the chemical composition of the fluids. Small precipitates formed on the coating surfaces when immersed in Ringers solution. These might account for the apparent drop in the degree of crystallinity when measured using X-ray diffraction. A significant drop in the interfacial adhesion was found for those coatings sprayed at high powers. This could be offset by prior precoating with a titanium bond coat and suitable heat treatment. In summary, the following processing sequence is suggested in order to achieve optimum coating properties: precoating the substrate with a layer of Ti (approximately 100 microm), spraying HA at a sufficiently high-power level (depending on particle size and gas mixture) and heat treatment at 700 degrees C for 1 h in air.

Adhesiveness↗

PubMed2002

Tribological study of lubricious DLC biocompatible coatings.

DLC (diamond-like carbon) coatings have remarkable tribological properties due mainly to their good frictional behavior. These coatings can be applied in many industrial and biomedical applications, where sliding can generate wear and frictional forces on the components, such as orthopaedic metal implants. This work reports on the development and tribological characterization of functionally gradient titanium alloyed DLC coatings. A PVD-magnetron sputtering technique has been used as the deposition method. The aim of this work was to study the tribological performance of the DLC coating when metal to metal contact (cobalt chromium or titanium alloys) takes place under dry and lubricated test conditions. Prior work by the authors demonstrates that the DLC coating reduced considerably the wear of the ultra-high-molecular-weight polyethylene (UHMWPE). The DLC coating during mechanical testing exhibited a high elastic recovery (65%) compared to the values obtained from Co-Cr-Mo (15%) and Ti-6Al-4V (23%). The coating exhibited an excellent tribo-performance against the Ti-6Al-4V and Co-Cr-Mo alloys, especially under dry conditions presenting a friction value of 0.12 and almost negligible wear. This coating has passed biocompatibility tests for implant devices on tissue/bone contact according to international standards (ISO 10993).

Journal Article↗

PubMed2001

A surface modified ODS superalloy by thermal oxidation for potential implant applications.

In the present work attention is paid on the composition, structure and protective properties of alumina layer produced by high temperature oxidation on MA 956 superalloy (Fe-20Cr-4.5Al-0.5Ti-0.5Y(2)O(3) (wt %)). The combination of good mechanical properties of this material and the excellent biocompatibility, the good wear and corrosion behavior of an outer alpha-alumina layer, limiting the release of ionic species and wear debris from the bulk material into the body-fluid environment, can make this material a candidate alloy for medical applications. Isothermal oxidation at 1100 degrees C in air of the alloy has led to the formation of a fine-grained, compact and adherent alpha-alumina scale. Oxide nodules rich in Ti, Y, Cr, and Fe were found on the top of the surface. In vitro electrochemical corrosion experiments showed good protective properties of the oxide scale. Moreover, no spallation of the alumina layer was observed. This feature is significant considering that the alumina layer has to withstand very high compressive stresses resulting from both growth and thermal stresses incorporated during cooling.

Journal Article↗