Influence of Surface Preparation of Aluminum Alloy AW-5754 and Stainless Steel X5CRNI18-10 on the Properties of Bonded Joints.

Adhesive bonding has proven to be a reliable method of joining materials, and the development of new adhesives has made it possible to use bonding in a variety of applications. This article addresses the challenges of bonding metals such as the aluminum alloy EN AW-5754 and the stainless steel X5CrNi18-10. In this study, the effects of laser cleaning and texturing on the surface properties and strength of two bonded joints were investigated and compared with mechanical preparation (hand sanding with Scotch-Brite and P180 sandpaper). The bonded joints were tested with three different epoxy adhesives. During the tests, the adhesion properties of the bonded surface were determined by measuring the contact angle and assessing the wettability, the surface roughness parameters for the different surface preparations, and the mechanical properties (tensile lap-shear strength). Based on the strength test results, it was found that bonded joints made of stainless steel had 16% to 40% higher strength than aluminum alloys when using the same adhesive and surface preparation. Laser cleaning resulted in maximum shear strength of the aluminum alloy bond, while the most suitable surface preparation for both materials was preparation with P180 sandpaper for all adhesives.

Creep Life Prediction of 10CrMo9-10 Steel by Larson-Miller Model.

Creep is defined as the permanent deformation of materials under the effect of sustained stress and elevated temperature for long periods of time, which can essentially lead to fracture. Due to very time-consuming and expensive testing requirements, existing experimental creep data are often analyzed using derived engineering parameters and models to predict and find the correlations between creep life (time to rupture), temperature and stress. The objective of this study was to analyze and compare different numerical algorithms by using the Larson-Miller parameter (LMP) extrapolation model. Calculations were performed using the classical LMP equation where different values of parameter C were selected, as well as using a modified LMP equation in which parameter C was stress dependent C(σ). The impact of two different approaches of extrapolation and correlation functions (linear and polynomial) applied to fit the LMP model was also investigated. A detailed analysis was performed to choose the best extrapolation fit function and error tolerance. The numerical algorithm implemented was validated through creep rupture testing performed on 10CrMo9-10 steel at 600 °C (873 K) and 80 MPa. Creep model behavior analysis proved that different values of C can significantly change the estimated time to rupture. An excellent response of the LMP model was obtained by considering polynomial dependency when parameter C was assumed to be 18, especially for the temperature range from 773 to 873 K. Promising results were also achieved when parameter C was taken as stress-dependent, but only for linear fitting, which requires further analysis. However, at validation stage it turned out that only the linear extrapolation function and C taken as a constant value provided adequate time-to-rupture prediction. In the case of C = 18, estimated time was slightly overestimated (~8%) and for C = 20 it was underestimated by 27%. In all other cases error largely exceeded 50%.

Influence of thermo-mechanical cycling on porcelain bonding to cobalt-chromium and titanium dental alloys fabricated by casting, milling, and selective laser melting.

PURPOSE: The aim has been to determine the effect of thermo-mechanical cycling on shear-bond-strength (SBS) of dental porcelain to Co-Cr and Ti-based alloys fabricated by casting, computer-numerical-controlled milling, and selective-laser-melting (SLM). METHODS: Seven groups (n=22/group) of metal cylinders were fabricated by casting (Co-Cr and commercially pure-cpTi), milling (Co-Cr, cpTi, Ti-6Al-4V) or by SLM (Co-Cr and Ti-6Al-4V) and abraded with airborne-particles. The average surface roughness (Ra) was determined for each group. Dental porcelain was applied and each metal-ceramic combination was divided into two subgroups - stored in deionized water (24-h, 37°C), or subjected to both thermal (6000-cycles, between 5 and 60°C) and mechanical cycling (105-cycles, 60N-load). SBS test-values and failure modes were recorded. Metal-ceramic interfaces were analyzed with a focused-ion-beam/scanning-electron-microscope (FIB/SEM) and energy-dispersive-spectroscopy (EDS). The elastic properties of the respective metal and ceramic materials were evaluated by instrumented-indentation-testing. The oxide thickness on intact Ti-based substrates was measured with Auger-electron-spectroscopy (AES). Data were analyzed using ANOVA, Tukey's HSD and t-tests (α=0.05). RESULTS: The SBS-means differed according to the metal-ceramic combination (p<0.0005) and to the fatigue conditions (p<0.0005). The failure modes and interface analyses suggest better porcelain adherence to Co-Cr than to Ti-based alloys. Values of Ra were dependent on the metal substrate (p<0.0005). Ti-based substrates were not covered with thick oxide layers following digital fabrication. CONCLUSIONS: Ti-based alloys are more susceptible than Co-Cr to reduction of porcelain bond strength following thermo-mechanical cycling. The porcelain bond strength to Ti-based alloys is affected by the applied metal processing technology.

Study of the provenance and technology of Asian kris daggers by application of X-ray analytical techniques and hardness testing.

Museum objects, such as the daggers presented in this study, contain a wealth of information regarding their role in certain historic periods, their potential users, the art of manufacture, the type of material used etc. Utilization of various modern instrumental techniques facilitates compositional information about the unknown artifact under investigation. In this study, a set of traditional Asian daggers called kris or keris, with scarce information about their entry into museum collections, their origin, the type of material used, the date of production, etc., were analysed by Energy Dispersive X-ray Fluorescence spectrometry (EDXRF), Proton Induced X-ray Emission (PIXE) and hardness measurements. In this way, the traditional procedure of historian inspection was supplemented by the scientific approach to obtain information about the artifacts.