C.R.F. Azevedo

Failure analysis of a commercially pure titanium plate for osteosynthesis

Abstract The failure of a titanium reconstruction plate for osteosynthesis, which occurred during use, was investigated. The plate was manufactured using commercially pure titanium. Microstructural examination revealed the presence of equiaxed α grains and intergranular platelets, which were identified as β phase. Fractographic examination revealed that fracture occurred by a fatigue mechanism associated with intense secondary intergranular cracking (brittle fracture). Selective attack of the β-precipitates was also observed on the surfaces of the implant, which were in contact with body fluids. The results indicated that the premature fracture of the plate was caused by a corrosion-fatigue mechanism.

Failure analysis of surgical implants in Brazil

Abstract The present paper summarises cases of metallurgical failure analysis of two femoral compression plates and one femoral nail-plate fabricated in stainless steel, one oral maxillo-facial plate for jaw reconstruction in commercially pure titanium alloy, and several Nitinol wires. The experimental work consisted of visual inspection of the samples, macroscopic and microscopic characterisation of the material, fractographic investigation of the fracture surface and adjacent areas and chemical composition. The present investigation revealed that most of the implants investigated were not in accordance with ISO standards and most of them presented evidence of corrosion assisted fracture. Additionally, some of the components revealed the presence of fabrication and/or processing defects, which contributed to their premature failure. The implantation of materials that are not biocompatible may cause several types of adverse effects in the human body and promote the premature failure of the implants, with immeasurable damages for the patients and losses for the public investment. The local sanitary regulation agencies are strengthening the mechanisms to avoid the commercialisation of surgical implants not in accordance with standards, including the adoption of retrieval analysis of failed implants.

Análise de falhas de implantes cirúrgicos no Brasil: a necessidade de uma regulamentação adequada

This paper summarizes several cases of metallurgical failure analysis of surgical implants conducted at the Laboratory of Failure Analysis, Instituto de Pesquisas Tecnológicas (IPT), in Brazil. Failures with two stainless steel femoral compression plates, one stainless steel femoral nail plate, one Ti-6Al-4V alloy maxillary reconstruction plate, and five Nitinol wires were investigated. The results showed that the implants were not in accordance with ISO standards and presented evidence of corrosion-assisted fracture. Furthermore, some of the implants presented manufacturing/processing defects which also contributed to their premature failure. Implantation of materials that are not biocompatible may cause several types of adverse effects in the human body and lead to premature implant failure. A review of prevailing health legislation is needed in Brazil, along with the adoption of regulatory mechanisms to assure the quality of surgical implants on the market, providing for compulsory procedures in the reporting and investigation of surgical implants which have failed in service.

Aircraft landing gear failure: fracture of the outer cylinder lug

Abstract The landing gear of an aircraft failed during landing due to the fracture of its outer cylinder attachment lug, which is manufactured from an aluminium alloy following British Specification DTD 5104 A. The material presented an oriented microstructure composed of bands of recrystallized and unrecrystallized grains. The unrecrystallized areas showed intense intragranular precipitation, while the recrystallized areas presented large primary precipitates and fine intergranular precipitation. Pit cavities associated with intergranular corrosion were observed along the perimeter line of the attachment bore surface and consumed preferentially the recrystallized areas of the microstructure. Fractographic examination revealed that the unstable crack propagation was originated in these stress raisers. The fracture mode is preponderantly ductile intergranular, with areas showing ductile fracture composed of small dimples. The results indicated that both corrosion and intergranular ductile crack propagation were favoured by the orientation of the microstructure, which was perpendicular to the free surface. Finally, the abnormal loads absorbed by the outer cylinder during the landing procedure associated with corrosion cavities located in a critical area may be concluded as the cause for this failure.

Characterisation of metallic piercings

Abstract The present investigation characterised five surgical stainless steel and one niobium piercings, which caused adverse reactions during use, culminating with the removal of the jewels. The results of chemical composition showed that none of the materials were in accordance with ISO (International Organization for Standardization) standards for metallic surgical implant materials. Additionally, none of the stainless steel piercings passed the pitting-resistance criterion of ISO 5832-1 standard, which implies that %Cr + 3.3×%Mo > 26. Most jewels revealed, under the microscope, intense linear irregularities on the surface. The lack of resistance to pitting corrosion associated with the poor surface finishing of the stainless steel jewels may induce localised corrosion, promoting the release of cytotoxic metallic ions, such as Cr, Ni and Mo, in the local tissue, which can promote several types of adverse effects in the human body, including allergic reactions. The adverse reaction to the niobium jewel could not be directly associated with the liberation of niobium ions nor the residual prescence of cytotoxic elements. The poor surface finish of the niobium jewel seems to be the only variable of the material, which may promote adverse reactions.

Archaeometry of ferrous artefacts from Luso-Brazilian archaeological sites near Ipanema River, Brazil

The present investigation analysed iron artefacts collected in two sites around Aracoaiaba Hill. A known methodology was adapted to investigate several samples collected at the Royal Iron Factory of Sao Joao do Ipanema and Sardinha sites. EDX microanalysis results of non-metallic inclusions were plotted in bivariate graphs. Linear regression (with and without the zero-intercept constraint) and line intercept significance tests were applied to interpret these results. The analysis did not allow the identification of the provenance of the production systems of Sardinha and Ipanema sites. The presence of Ti-rich inclusions was an unambiguous attribute of the samples collected at the Sardinha site.

Assessment of the Ti-rich corner of the Ti-Si phase diagram using two sublattices to describe the Ti5Si3 phase

The thermodynamic optimization of Ti-X-Si systems requires that their respective binary systems be constantly updated. The most recent assessments of the Ti-Si phase diagrams used three sublattices to describe the Ti5Si3 phase. The stable version of this phase diagram indicated the presence of Ti(β)+Ti5Si3→Ti3Si and Ti(β)→Ti(α)+Ti3Si reactions in the Ti-rich corner, while the metastable version featured the presence of a Ti(β)→Ti(α)+Ti5Si3 reaction. The present investigation assessed these phase diagrams using two sublattices to describe the Ti5Si3 phase in order to simplify the optimization of Ti-X-Si systems.

SIMPLIFICATION OF THE THERMODYNAMIC DESCRIPTION OF THE Ti-Si SYSTEM

The thermodynamic optimization of ternary or higher order systems containing Ti requires that the Ti-X binary systems are continuously updated. The Ti-Si system has been studied and thermodynamically optimized since de 1950s. The Ti5Si3 phase was initially considered stoichiometric to facilitate the thermodynamic calculations, although experimental results showed that this phase was a non-stoichiometric intermetallic. The most recent optimization of the Ti-Si system described this phase as a non-stoichiometric intermetallic with three sublattices, using the sub-lattice model. The problem of this approach is that it increases considerably the number of variables to be optimized during the calculation of the Ti-Si-X phase diagrams, hindering the convergence of the computational processing. The present work simplifies the optimization of the Ti-Si system, assuming that Ti5Si3 phase is mostly hyper-stoichiometric in relation to Ti. The results showed that this simplification did not significantly affect the phase diagram and the thermodynamic properties calculated for the system.

Effect of solution heat treatment on the pitting corrosion behavior of a high Mn austenitic stainless steel in chloride solution

The effect of solution heat treatment on the pitting corrosion resistance of 17Cr-6Mn-5Ni-1.5Cu austenitic stainless steel in 0.6M NaCl aqueous solution was evaluated. UNS S30403 (304L) steel was used as benchmark material. Solution heat treatments (SHT) were conducted at 1010°C, 1040°C, 1070°C and 1100°C. The microstructural characterization revealed the presence of δ-ferrite, especially in the asreceived condition (AR). The SHT decreased the proportion of the ferrite phase. Mnrich precipitates were observed in the as-received condition of 17Cr-6Mn-5Ni-1.5Cu steel, but they were dissolved after the SHT, causing localized Mn enrichment in the austenite. Potentiodynamic tests showed that the pitting potential (Ep) in the 304L steel was not altered significantly after SHT. On the other hand, the value of Ep of the 17Cr-6Mn-5Ni-1.5Cu steel decreased after SHT. This detrimental effect was explained by the formation of Mn enrichment areas due to the solubilization of Mn-rich precipitates, which promoted preferential Cl- adsorption in these regions.