The effects of severe plastic deformation on some properties relevant to Ti implants

In some types of surgical implants, such as bone screws and plates, Grade 2 Ti is seriously considered as a replacement for the Ti-6Al-4V alloy. Advantages are lower cost and the absence of Al and V, which have been identified as potentially harmful to human health. The present paper shows that the lower strength of the commercially pure metal can be enhanced by Severe Plastic Deformation followed by conventional cold rolling, so as to reach a strength level higher than the technical requirements applicable to the alloy. This was ascertained by tensile and Vickers hardness tests from which it was concluded that the best combination of properties are obtained by submitting the metal to Equal Channel Angular Pressing (four passes at 300 °C) followed by a 70% thickness reduction by cold rolling. Although the present results are valid for the material only, and not for the product considered, that is, bone screws, it appears that this solution is a step towards the replacement of the Ti6-4 alloy by Grade 2 Ti, at least for some types of metallic medical implants

Constant load creep data in air and vacuum on 2.25Cr-1Mo steel from 600 °C to 700 °C

Creep results on 2.25Cr-1Mo were obtained at 600 °C, 650 °C and 700 °C at five stress levels, under constant load, in air and vacuum. Two chambers were specially developed for carrying out creep testing in controlled environment, with the possibility of accommodating inside them the load train, the extensometry system and the thermocouples. The creep machines used in this project present the advantage of allowing the performance of both constant load or constant stress creep testing, using interchangeable profiles. The preliminary set of constant load data reported here was analyzed according to the conventional methodology of creep data analysis, with the identification of parameters of the Norton, Arrhenius, Monkman-Grant and some extrapolation relations involving stress, temperature, minimum creep rate and rupture time. The results indicate a strong effect of the oxidation phenomenon on the creep behavior of this steel. The data were consistent and meaningful so that the developed chambers can be considered to present good performance in the generation of creep data in vacuum

Microstructural development and tensile strength of an ECAP: deformed Al-4 wt. (%) Cu alloy

The tensile strength of metals and alloys can be considerably increased by severe plastic deformation, a consequence of the extreme grain refinement thus achieved. In the present work the deformation was performed by Equal Channel Angular Pressing and the material was an Al-4% Cu alloy. Characterization included tensile tests, and microstructural observation by optical and transmission electron microscopy. After four passes, the yield strength showed an increase of 310% over the undeformed alloy, a figure reduced to 160% by a 250 °C / 1 hour post - deformation anneal. Additionally, the alloy displayed a very low work hardening capacity, especially after the annealing heat treatment. After four deformation passes the grain size of the annealed specimens was estimated to be close to 500 nm. The tensile behaviour and the absence of work hardening were discussed in terms of the fine microstructure

The effects of severe plastic deformation on some properties relevant to Ti implants

In some types of surgical implants, such as bone screws and plates, Grade 2 Ti is seriously considered as a replacement for the Ti-6Al-4V alloy. Advantages are lower cost and the absence of Al and V, which have been identified as potentially harmful to human health. The present paper shows that the lower strength of the commercially pure metal can be enhanced by Severe Plastic Deformation followed by conventional cold rolling, so as to reach a strength level higher than the technical requirements applicable to the alloy. This was ascertained by tensile and Vickers hardness tests from which it was concluded that the best combination of properties are obtained by submitting the metal to Equal Channel Angular Pressing (four passes at 300 °C) followed by a 70% thickness reduction by cold rolling. Although the present results are valid for the material only, and not for the product considered, that is, bone screws, it appears that this solution is a step towards the replacement of the Ti6-4 alloy by Grade 2 Ti, at least for some types of metallic medical implants

Investigation of Stress Status in the Micro-Space of Surface and Subsurface Layer

One of main issues when evaluating or analysing quality and functional properties of work-piece is identification of status of residual stress. Every treatment or machining process generates residual stress in the surface and subsurface layers of the material structure. The residual stress has a large influence on the functional properties of the components. The article is focused on the method of triaxial measurement of residual stress after machining the surface of sample by high feed milling technology. Significance of triaxial measuring is the capability of measuring in different angles so it is possible to acquire stress tensor containing normal and shear stress components acting in the spot of measuring, using a Cartesian coordinate system

A general study of commercially pure Ti subjected to severe plastic deformation: microstructure, strength and corrosion resistance

A general study of commercially pure Ti subjected to severe plastic deformation: microstructure, strength and corrosion resistanc

Numerical simulation of cryogenic cyclic closed-die forging of Cu: hardness distribution, strain maps and microstructural stability

Cyclic closed-die forging (CCDF) appears to be an easy to operate deformation process, which imposes high levels of strain, even on difficult-to-deform materials. However, despite said potential advantages, the CCDF at cryogenic temperatures has not yet been investigated. Copper samples with dimensions of 10 mm × 10 mm × 20 mm were processed in up to six passes with interpass rotation, enabling the samples to return approximately to their initial dimensions after each pass. The intensity and homogeneity of plastic deformation was evaluated by mapping the Vickers hardness over the entire surface of the sample, and the resulting maps were compared with the strain and stress distribution estimated by FEM numerical simulation. The deformed microstructures were examined by optical and transmission electron microscopy. Cryogenic CCDF has proved to be effective in suppressing the recovery mechanisms of Cu samples, resulting in finer and more heterogeneous strains distribution than those deformed at room temperature. However, long-term observations by TEM have shown that these microstructures are inherently unstable, so that hardness decreases 50% after two years. Keywords: Copper, Cyclic closed-die forging, Numerical simulation, Cryogenic deformation, Microstructural stabilit

Severe plastic deformation by equal channel angular pressing: product quality and operational details

As a technique, Equal Channel Angular Pressing (ECAP) is simple and inexpensive. However, if die manufacture and operational details are not carefully planned and implemented, difficulties arise, which can interfere with the product characteristics and the pressing operation itself. The present paper offers guidelines on die design and manufacture, emphasizing geometry, material and heat treatment. Further, operational parameters such as lubrication, pressing temperature, deformation routes, die closure procedure and the influence of channel cross section on maximum acceptable load are described. Additionally, the effects of those variables on the product characteristics (deformation level and homogeneity) and integrity, plus process control and safety, are discussed

The effect of preheating temperature on the forming limit diagram of AA1050/AA7050 Al multilayered sheets produced by accumulative roll bonding (ARB)

Multilayered sheets of AA1050 and AA7050 Al alloys produced by hot accumulative roll bonding (ARB) are tested to estimate their forming limit diagrams (FLDs). Sheets processed with preheating at 450 and 500¿°C for up to six ARB cycles are submitted to Nakazima tests with an in situ digital image correlation system and tensile tests to analyze the mechanical behavior. X-ray measurements and electron backscatter diffraction are performed to obtain the crystallographic texture and the mesotexture, respectively, and thus characterize the heterogeneous microstructure. A bimodal grain size distribution is observed in these sheets since AA7050 layers present elongated and fine grain size with nanometric precipitates and AA1050 layers present coarser and equiaxed grains. In addition, texture analysis indicates both rolling and shear components in the sheets. The FLDs show that the forming properties did not follow the expected rule of mixtures when compared with monolithic alloy sheets. Overall, the multilayered AA1050/AA7050 processed by means of ARB at 500¿°C presents better formability than that at 450¿°C, due to the combination of lower anisotropy measured by the Lankford coefficients values close to 1 and low normal anisotropy ¿r values.Peer ReviewedPostprint (author's final draft