Key Engineering Materials Vol. 586

Abstract: The paper presents the results of strain measurement using two methods: videoextensometry (ME46) and digital image correlation (DIC)-ARAMIS. ME46 - allows measuring and monitoring the major and minor strain on a planar surface of a loaded object [1]. Experimental equipment uses a CCD camera for monitoring the process. The software calculates the displacements of contrast dots and subsequently the strain components are obtained. Another method for non-contact measurements is DIC technique; the measurements are done using three-dimensional image correlation system. The system uses two digital high-speed cameras providing a synchronized stereo view of the specimen where speckles are arranged on the surface. The results show the complete strain field during the tests, including details of the strain field when necking develops prior to the failure [2]. Experimental results obtained on ultra high strength automotive steels DP 1000 and 1400M grades during static tensile test are presented in the paper. The outputs of both are deformation maps. Advantages and disadvantages of both methods are compared.

Abstract: The indentation methods (HR15N, HV0.3, HIT, EIT) were used to evaluate differences between the WC-based coatings with 12, 17 and 25% of Co binder. The two sets of WC-12%Co coatings with two different sets of parameters were sprayed to evaluate the influence of spraying parameters. The measured mechanical characteristic were correlated to the to the wear resistance of the coatings evaluated by dry sand/rubber wheel test according to ASTM G-65 and pin-on disc according to ASTM G-99. The measured results showed that there is almost no difference between the abrasive wear resistance of WC-Co coating with 12 and 17% of Co binder, while the wear of coating with 25% of Co binder is significantly higher. The importance of the spraying parameters on the WC-12%Co coatings properties has been found to be comparable to the importance of binder content influence.

Abstract: Secondary aluminium alloys are made out of aluminium scrap and aluminium-processable waste by recycling. These alloys contain different alloying elements such as Al, Cu, Fe, Si and Mg that form intermetallic phases in aluminium matrix and influence on the microstructure, basic mechanical properties and microhardness evolution in aluminium cast alloy. As experimental material was used secondary aluminium cast alloy AlSi9Cu3. Material was subjected to heat treatment (age-hardening) consisting of a solution treatment at temperature 515 °C with holding time 4 hours, than water quenching at 40 °C and artificial aging by different temperature 130 °C, 150 °C and 170 °C with different holding time (2, 4, 8, 16 and 32 hours). The age-hardening led to changes in the morphology of structural components, but also leads to precipitation of finer hardening phases in the material substructure. As optimal age-hardening mode for secondary aluminium cast alloy AlSi9Cu3 was determined mode consisting of solution treatment at temperature 515 °C with holding time 4 hours and artificial aging at temperature 170 °C with holding time 16 hours. After this heat treatment cast alloy shows the best changes in microstructure and mechanical properties. These changes are comparable with changes by primary AlSi9Cu3 cast alloy.

Abstract: The stability of the microstructure and properties of the iron superalloys of the secondgeneration IN 519 (24% Cr, 24% Ni, 1.5% Nb) modified with 0.1 and 0.2 [wt.%] rare earthelements was investigated. The alloys underwent annealing at 825 oC for 10, 100 and 1000 h. Thefollowing techniques were used to evaluate the phase transformation: X-ray diffraction on crosssectionand isolates extracted from the as-cast and annealed alloys, microstructure analysis byoptical microscopy, hardness measurements by Brinell and nanoindentation with a Berkovich tipmethod. The analysis of changes in hardness distribution due to thermal processing of superalloyswas conducted with respect to the average hardness of matrix and phase precipitates.

Abstract: The paper presents a methodology for the lifetime assessment of welded polymer pipes. A fracture mechanics analysis of a butt-welded joint is performed by simulating radial crack growth in the nonhomogenous region of the pipe weld. It was found that the presence of material nonhomogeneity in the pipe weld caused by the welding procedure leads to an increase in the stress intensity factor of the radial crack and changes the usual failure mode of the pipe system. This can lead to a significant reduction in the lifetime of the pipe system.

Abstract: The contribution deals with evaluation of mechanical properties of thin hard coatings prepared by ARC evaporation on steel substrate K110. In this paper TiN and AlTiCrN are comparatively studied. The thickness of TiN and AlTiCrN coatings was evaluated using the calotest, GDOES and nanohardness was also measured. The results show that AlTiCrN coatings posses higher hardness and Young´s modulus than simple monolayer TiN coatings. The substrate-coating interface was without failures, which confirmed excellent adhesion properties of the system. Due to their specific properties, the coatings appear suitable for use in practical operations.

Abstract: This article deals with testing of fatigue properties of hardened gears at bending. These tests are defined by the standard ISO 6336 - method B, when testing is carried out under reference conditions close to the real operation. This type of testing may be helpful to evaluate the influence of new materials, design parameters, production technology, or the effects of surface finishing. The first part of this article deals with the theory of fatigue testing methodology using modified stair-case method and characteristics of the testing machine. The second part of the paper is devoted to the characteristics of the experimental material and the results achieved. The case hardened steel gears alloyed by Cr-Ni-Mo were selected for the experiment. Hardened gears were subjected to local hardness measurement and subsequently the bending fatigue tests were performed. Ruptured samples were analyzed using a scanning electron microscope. The local bending stress was determined using the modified computational model based on the ISO 6336 standard methodology. The focus of this work consisted in evaluation of the influence of the filler root surface treatment on fatigue limit at bending on the basis of the realized experiments and their confrontation with the equivalents specified in the standards ISO 6336 and ČSN 01 4686.

Abstract: Structural relaxation an creep strain recovery of the amorphous metallic glass Fe40Ni41B19 after the longtime loading at different annealing temperatures below the glass transition temperature have been studied using anisothermal differential scanning calorimetry (DSC) and dilatometry (TMA). It has been demonstrated that structural relaxation effects depend on the stress-annealing temperature of the amorphous ribbon. The influence of the stress-annealing temperature on the rearrangement of deformation defects in the amorphous alloy Fe-Ni-B was analyzed. The properties of local disordering in flow defects were analyzed by means of their activation energy spectra. In the samples stress-annealed at higher temperatures, only the relaxation centers favourably oriented to the external stress contribute to the creep strain recovery process.

Abstract: The resistance spot welding of dissimilar materials is generally more challenging than that of similar materials due to differences in the physical, chemical and mechanical properties of the base metals. Advanced high strength steels and high strength low alloy steels are utilized in automotive industry to reduce weight of the vehicle body and consequently lowering the fuel consumption to achieve the lowest possible fuel consumption, high active and passive safety of passengers while decreasing the amount of emission. The influence of the primary welding parameters, especially welding current, microhardness and tensile shear load bearing capacity of dissimilar welds between TRIP 40/70 as an Advanced High Strength Steel and H220PD as a High-Strength Low-Alloy steel has been investigated in this paper.

Abstract: Mechanical properties of porous silicon nitride prepared by two different processing routes have been studied. Depth sensing methods was used to measure the hardness and elastic modulus of experimental materials. The results were compared with the hardness and elastic modulus of trabecular bone in order to find out porous ceramics with properties close to that of trabecular bone. Material prepared by infiltration of polyurethane sponge exhibited properties close to the properties of bone and it is the potential material for further investigation in the bioapplication field.