Influence of the cutting edge micro-geometry of PCBN tools on the flank wear in orthogonal quenched and tempered turning M2 steel

Quenched and tempered high-speed steels obtained by powder metallurgy are commonly used in automotive components, such as valve seats of combustion engines. In order to machine these components, tools with high wear resistance and appropriate cutting edge geometry are required. This work aims to investigate the influence of the edge preparation of polycrystalline cubic boron nitride (PCBN) tools on the wear behavior in the orthogonal longitudinal turning of quenched and tempered M2 high-speed steels obtained by powder metallurgy. For this research, PCBN tools with high and low-CBN content have been used. Two different cutting edge geometries with a honed radius were tested: with a ground land (S shape) and without it (E shape). Also, the cutting speed was varied from 100 to 220 m/min. A rigid CNC lathe was used. The results showed that the high-CBN, E-shaped tool presented the longest life for a cutting speed of 100 m/min. High-CBN tools with a ground land and honed edge radius (S shaped) showed edge damage and lower values of the tool’s life. Low-CBN, S-shaped tools showed similar results, but with an inferior performance when compared with tools with high CBN content in both forms of edge preparation.

Elucidating the interactions between the adhesive and transcriptioanl functions of beta-catenin in normal and cancerous cells

Wnt signalling is involved in a wide range of physiological and pathological processes. The presence of an extracellular Wnt stimulus induces cytoplasmic stabilisation and nuclear translocation of beta-catenin, a protein that also plays an essential role in cadherin-mediated adhesion. Two main hypotheses have been proposed concerning the balance between beta-catenin's adhesive and transcriptional functions: either beta-catenin's fate is determined by competition between its binding partners, or Wnt induces folding of beta-catenin into a conformation allocated preferentially to transcription. The experimental data supporting each hypotheses remain inconclusive. In this paper we present a new mathematical model of the Wnt pathway that incorporates beta-catenin's dual function. We use this model to carry out a series of in silico experiments and compare the behaviour of systems governed by each hypothesis. Our analytical results and model simulations provide further insight into the current understanding of Wnt signalling and, in particular, reveal differences in the response of the two modes of interaction between adhesion and signalling in certain in silico settings. We also exploit our model to investigate the impact of the mutations most commonly observed in human colorectal cancer. Simulations show that the amount of functional APC required to maintain a normal phenotype increases with increasing strength of the Wnt signal, a result which illustrates that the environment can substantially influence both tumour initiation and phenotype.

Manufacturing conditioned roughness and wear of biomedical oxide ceramics for all-ceramic knee implants

Background: Ceramic materials are used in a growing proportion of hip joint prostheses due to their wear resistance and biocompatibility properties. However, ceramics have not been applied successfully in total knee joint endoprostheses to date. One reason for this is that with strict surface quality requirements, there are significant challenges with regard to machining. High-toughness bioceramics can only be machined by grinding and polishing processes. The aim of this study was to develop an automated process chain for the manufacturing of an all-ceramic knee implant. Methods: A five-axis machining process was developed for all-ceramic implant components. These components were used in an investigation of the influence of surface conformity on wear behavior under simplified knee joint motion. Results: The implant components showed considerably reduced wear compared to conventional material combinations. Contact area resulting from a variety of component surface shapes, with a variety of levels of surface conformity, greatly influenced wear rate. Conclusions: It is possible to realize an all-ceramic knee endoprosthesis device, with a precise and affordable manufacturing process. The shape accuracy of the component surfaces, as specified by the design and achieved during the manufacturing process, has a substantial influence on the wear behavior of the prosthesis. This result, if corroborated by results with a greater sample size, is likely to influence the design parameters of such devices.

A rolling-gliding wear simulator for the investigation of tribological material pairings for application in total knee arthroplasty

Background: Material wear testing is an important technique in the development and evaluation of materials for use in implant for total knee arthroplasty. Since a knee joint induces a complex rolling-gliding movement, standardised material wear testing devices such as Pin-on-Disc or Ring-on-Disc testers are suitable to only a limited extent because they generate pure gliding motion only.Methods: A rolling-gliding wear simulator was thus designed, constructed and implemented, which simulates and reproduces the rolling-gliding movement and loading of the knee joint on specimens of simplified geometry. The technical concept was to run a base-plate, representing the tibia plateau, against a pivoted cylindrical counter-body, representing one femur condyle under an axial load. A rolling movement occurs as a result of the friction and pure gliding is induced by limiting the rotation of the cylindrical counter-body. The set up also enables simplified specimens handling and removal for gravimetrical wear measurements. Long-term wear tests and gravimetrical wear measurements were carried out on the well known material pairings: cobalt chrome-polyethylene, ceramic-polyethylene and ceramic-ceramic, over three million motion cycles to allow material comparisons to be made.Results: The observed differences in wear rates between cobalt-chrome on polyethylene and ceramic on polyethylene pairings were similar to the differences of published data for existing material-pairings. Test results on ceramic-ceramic pairings of different frontal-plane geometry and surface roughness displayed low wear rates and no fracture failures.Conclusions: The presented set up is able to simulate the rolling-gliding movement of the knee joint, is easy to use, and requires a minimum of user intervention or monitoring. It is suitable for long-term testing, and therefore a useful tool for the investigation of new and promising materials which are of interest for application in knee joint replacement implants. © 2010 Richter et al; licensee BioMed Central Ltd.

Sodium hypochlorite effects on dentin bond strength and acid-base resistant zone formation by adhesive systems

Aim: To evaluate the effects of 10% NaOCl gel application on the dentin bond strengths and morphology of resin-dentin interfaces formed by three adhesives. Methods: Two etch-and-rinse adhesives (One-Step Plus, Bisco Inc. and Clearfil Photo Bond, Kuraray Noritake Dental) and one self-etch adhesive (Clearfil SE Bond, Kuraray Noritake Dental) were applied on dentin according to the manufacturers’ instructions or after the treatment with 10% NaOCl (ED-Gel, Kuraray Noritake Dental) for 60 s. For interfacial analysis, specimens were subjected to acid-base challenge and observed by SEM to identify the formation of the acid-base resistant zone (ABRZ). For microtensile bond strength, the same groups were investigated and the restored teeth were thermocycled (5,000 cycles) or not before testing. Bond strength data were subjected to two-way ANOVA and Tukey’s test (p<0.05). Results: NaOCl application affected the bond strengths for One-Step Plus and Clearfil Photo Bond. Thermocycling reduced the bond strengths for Clearfil Photo Bond and Clearfil SE Bond when used after NaOCl application and One-Step Plus when used as recommended by manufacturer. ABRZ was observed adjacent to the hybrid layer for self-etch primer. The etch-and-rinse systems showed external lesions after acid-base challenge and no ABRZ formation when applied according to manufacturer’s instructions. Conclusions: 10% NaOCl changed the morphology of the bonding interfaces and its use with etch-&-rinse adhesives reduced the dentin bond strength. Formation of ABRZ was material-dependent and the interface morphologies were different among the tested materials.

Influence of adhesive system on quartz fiber post dislocation resistance in endodontically treated teeth

Aim: To evaluate the dislocation resistance of the quartz fiber post/cement/dentin interface after different adhesion strategies. Methods: Forty bovine lower central incisors were selected and prepared with K-files using the step-back technique, and irrigated with 3 mL of distilled water preceding the use of each instrument. Prepared teeth were stored at 37ºC and 100% humidity for 7 days. The roots were prepared and randomized into 4 groups. The quartz fiber post was cemented with an adhesion strategy according to the following groups: GBisCem- BISCEM; GOneStep±C&B- One Step ± C&B; GAllBond±C&B- AllBond3 ± C&B; GAllBondSE±C&B- AllBondSE ±C&B with a quartz fiber post. Cross-sectional root slices of 0.7 mm were produced and stored for 24 h at 37° C before being submitted to push-out bond strength. Results: The mean and standard deviation values of dislocation resistance were GBisCem: 1.12 (± 0.23) MPa, GOneStep±C&B: 0.81 (± 0.31) MPa, GAllBond±C&B: 0.98 (± 0.14) MPa, and GAllBondSE±C&B: 1.57 (± 0.04) MPa. GAllBondSE±C&B showed significantly higher values of dislocation resistance than the other groups. Conclusions: Based on this study design, it may be concluded that adhesion strategies showed different results of quartz post dislocation resistance. Simplified adhesive system with sodium benzene sulphinate incorporation provided superior dislocation resistance.

Antimicrobial and bond strength properties of a dental adhesive containing zinc oxide nanoparticles

Aim: To assess the effect of adding zinc oxide nanoparticles to dental adhesives on their anti-microbial and bond strength properties. Methods: 45 human premolars were cut at the cement enamel junction (CEJ) and the crowns were sliced into buccal and lingual halves. The specimens were classified into three groups, etched with 37% phosphoric acid for 15 s and rinsed for 30 s. Single Bond, Single Bond+5% zinc oxide and Single Bond+10% zinc oxide were used in the first, second and third groups. A cylinder of Z250 composite was bonded and cured for 40 s. For anti-bacterial testing, 10 samples of each group were assessed by direct contact test; 10 μL of bacterial suspension was transferred into tubes containing adhesives and incubated for one hour; 300 μL of brain heart infusion (BHI) broth was added to each tube and after 12 h, 50 μL of bacteria and broth were spread on blood agar plates and incubated for 24 h. Results: The colony count decreased significantly in the second and third groups compared to the first. Conclusions: Incorporation of zinc oxide nanoparticles into dental adhesives increases their anti-microbial properties without affecting their bond strength.

Effect of particle characteristics on the two-body abrasive wear behaviour of a pearlitic steel

The specific wear rate and friction coefficient of a pearlitic microstructure subjected to different abrasive environments (i.e. SiC and alumina) were examined. A CSM high temperature pin-on-disc tribometer was used to simulate the two-body abrasive condition (i.e. the metallic surface abrading against the abrasive particles). The characteristics of the abrasive particles (i.e. particle size and density) revealed a significant impact on the amount of material loss. The specific wear rate of the pearlitic microstructure decreased with a reduction in the abrasive particle size, irrespective of the particle type. In addition, distinct particle deterioration mechanisms were observed during the abrasion process, which was largely determined by the abrasive particle size. Attrition, shelling and fracture were some of the dominant particle deterioration mechanisms occurring in both of the abrasive environments. SEM and EDX analysis on the wear debris displayed a unique metallic chip formation with respect to the particle type. Furthermore, the abrading efficiency (i.e. threshold level) of the abrasive particles was identified by means of interrupted abrasive wear tests. The dense packing nature of the alumina abrasive particles resulted in a significantly higher material removal rate than the SiC abrasive environment.

Comparisons of the two-body abrasive wear behaviour of four different ferrous microstructures with similar hardness levels

The abrasive wear resistance of four distinct metallurgical steel microstructures - bainite, pearlite, martensite and tempered martensite, with similar hardness levels was investigated. A pin-on-disc tribometer was used to simulate the two-body abrasive condition (i.e. the metallic surface abrading against the silicon carbide abrasive particles) and evaluate the specific wear rate of the microstructures. Each microstructure had a unique response towards the abrasion behaviour and this was largely evident in the friction curve. However, the multi-phase microstructures (i.e. bainite and pearlite) demonstrated better abrasion resistance than the single-phase microstructures (i.e. martensite and tempered martensite). Abrasion induced microstructural changes at the deformed surfaces were studied using sub-surface and topographical techniques. The properties of these layers (i.e. surface profile measurements) determined the amount of material loss for each microstructure. These were directly linked to the single-wear track analysis that highlighted a marked difference in their mode of material removal. Ploughing and wedge formation modes were dominant in the case of bainite and pearlite microstructures, whereas the cutting mode could be attributed to the higher material loss in the single-phase microstructures. The combination of brittle and ductile phases in the multi-phase microstructure matrix could be one of the driving factors for their superior abrasion resistance.

Effect of retained austenite on wear resistance of nanostructured dual phase steels

Nanostructured super bainitic and quenching-partitioning (Q&P) martensitic steels with a significant amount of retained austenite obtained by low temperature bainitic transformation and Q&P respectively were studied to explore the effect of retained austenite on stirring wear resistance. The results suggest that the Q&P martensitic steel significantly enhanced the hardness of the worn surface (from 674 to 762 HV1) and increased the thickness of the deformed layer (,3.3 mm), compared to the nanostructured bainitic steel. The underlying reason is that the Q&P martensitic steel has a higher stability of retained austenite thereby providing a superior transformation induced plasticity effect to increase surface hardness and reduce wear rate during the wear process.

The impact of retained austenite characteristics on the two-body abrasive wear behavior of ultrahigh strength bainitic steels

In the current study, a high-carbon, high-alloy steel (0.79 pct C, 1.5 pct Si, 1.98 pct Mn, 0.98 pct Cr, 0.24 pct Mo, 1.06 pct Al, and 1.58 pct Co in wt pct) was subjected to an isothermal bainitic transformation at a temperature range of 473 K to 623 K (200 °C to 350 °C), resulting in different fully bainitic microstructures consisting of bainitic ferrite and retained austenite. With a decrease in the transformation temperature, the microstructure was significantly refined from ~300 nm at 623 K (350 °C) to less than 60 nm at 473 K (200 °C), forming nanostructured bainitic microstructure. In addition, the morphology of retained austenite was progressively altered from film + blocky to an exclusive film morphology with a decrease in the temperature. This resulted in an enhanced wear resistance in nanobainitic microstructures formed at low transformation temperature, e.g., 473 K (200 °C). Meanwhile, it gradually deteriorated with an increase in the phase transformation temperature. This was mostly attributed to the retained austenite characteristics (i.e., thin film vs blocky), which significantly altered their mechanical stability. The presence of blocky retained austenite at high transformation temperature, e.g., 623 K (350 °C) resulted in an early onset of TRIPing phenomenon during abrasion. This led to the formation of coarse martensite with irregular morphology, which is more vulnerable to crack initiation and propagation than that of martensite formed from the thin film austenite, e.g., 473 K (200 °C). This resulted in a pronounced material loss for the fully bainitic microstructures transformed at high temperature, e.g., 623 K (350 °C), leading to distinct sub-surface layer and friction coefficient curve characteristics. A comparison of the abrasive behavior of the fully bainitic microstructure formed at 623 K (350 °C) and fully pearlitic microstructure demonstrated a detrimental effect of blocky retained austenite with low mechanical stability on the two-body abrasion.

Tool wear and surface integrity analysis of machined heat treated selective laser melted Ti-6Al-4V

In this study, the tool wear and surface integrity during machining of wrought and Selective LaserMelted (SLM) titanium alloy (after heat treatment) are studied. Face turning trails were carried out onboth the materials at different cutting speeds of 60,120 and 180 m/min. Cutting tools and machinedspecimens collected are characterized using scanning electron microscope, surface profiler and opticalmicroscope to study the tool wear, machined surface quality and machining induced microstructuralalterations. It was found that high cutting speeds lead to rapid tool wear during machining of SLMTi-6Al-4V materials. Rapid tool wear observed at high cutting speeds in machining SLM Ti-6Al-4Vresulted in damaging the surface integrity by 1) Deposition of chip/work material on the machinedsurface giving rise to higher surface roughness and 2) Increasing the depth of plastic deformationon the machined sub surface.