Solid State Phenomena Vol. 216

Abstract: Tools for plastic deformation at hot or cold are made of medium or high alloyed special steels, which are relatively expensive. To reduce the material costs of these tools, it is possible to manufacture them of low alloyed steels. In this case it was used steel 42CrMo4 (1.7225). The active surface of these tools is carried out by charging a welding wear resistant material. Within the framework of research it was used the VTCr25W4TiLa filler material, made in the form of tubular rod designed for WIG process deposits or oxyacetylene flame of wear-resistant layers. Anti-wear layers made austenitic structure, in which fine carbides of Cr, W and Ti are embedded. These layers are characterized by high abrasion resistance , combined with corrosion resistance and thermomechanical fatigue. Depending on the heat treatment applied can be obtained usable tools for plastic deformation at hot or cold.

Abstract: Titanium based bulk metallic glasses (BMGs) are characterized by properties such as high corrosion resistance, Youngs modulus, hardness, fracture strength and wear resistance that recommend them as performant biomaterials for orthopedics and dentistry. Present researches have been focused on some Ti-Zr-Cu-Ga-Si-Sn alloy which could be feasible alternative to almost classical nickel containing BMGs. has been casted by vacuum suction in a copper mold. Suction casting has been used to produce by mean of ultra-rapid cooling experimental samples as 2mm cylinders, and complex investigation program based on optical microscopy, SEM, and HR-TEM techniques has been performed to characterize resulting microstructure. Although presence of gallium produces considerable difficulties in sample preparation, investigations based on high resolution transmission electron microscopy (HR-TEM) have evidenced simultaneous presence of amorphous, crystalline and partially crystalline structures.

Abstract: The purpose of the study was to investigate the microchemical, morphological, mechanical and anticorrosive characteristics of the metallic brackets by using energy-dispersive X-ray spectroscopy (EDS), scanning electron microscopy (SEM), electrochemical and shear tests. The changes resulted from the exposure of the metallic brackets to artificial saliva and debonding forces were investigated under orthodontic appliances. The results have shown that metallic brackets studied in this paper present a good design, great electrochemical behaviour in artificial saliva for different pH values (2, 5 and 7), and also great mechanical properties. In the case of shear stress the obtained values were higher than the clinical accepted value. The metallic brackets studied in this paper present a good behaviour in artificial saliva, and good mechanical characteristics. The ARI investigation revealed that most of the adhesive was left on the bracket.

Abstract: The aim of this work is to understand the evolutions of the β₁ metastable austenite phase of a CuAlBe Shape Memory Alloy at macroscopic and microscopic scales under mechanical solicitation by neutron diffraction. The tensile specimen, taken in the raw material is subjected to superelastic cycles at room temperature on SMARTS diffractometer. Before loading, the mater ial is fully austenitic. During loading, after elastic deformation of austenite, phase transformation starts, martensite variants appear. The material follows a law of pseudo elastic behavior. At the end of the first mechanical cycle after unloading, the macroscopic curve does not fully return into its original point. A macroscopic deformation is observed. The evolution of first order microdeformations during mechanical cycles shows a large deformation of {400} plane family. This deformation is linked to the presence of <001> partial fibber characterizing the crystallographic texture of the material after elaboration. The FWHM of the (400) diffraction peak is also largely increased during loading. This increase is the signature of the generation of stacking faults during the transformation of β₁ metastable austenite into β₁ martensite.

Abstract: The paper investigates the causes that led to the premature failure of a crankshaft (approximately 200 hours) from an engine used in equipment that worked on a construction site for concrete pumping. Microscopic analysis (optic and electronic), chemical and macroscopic investigations were conducted in order to find the causes of breakage of the crankshaft.

Abstract: The present paper aims to study the possibility to modify the properties of polyvinyl alcohol (pva) cryogels prepared in the presence of ketoprofen in order to replace the damaged articular cartilage. Articular cartilage is the most important part of articulation characterized by very low friction, high wear resistance, and poor regenerative qualities. Polyvinyl alcohol is a non-expensive polymer, versatile and adaptable to various needs, with exceptional properties such as water solubility, biocompatibility, non-toxicity and with capability to form hydrogels by chemical or physical methods. The aims of this paper are the synthesis, the physicochemical characterization and analysis of the tribological properties of pva cryogels for cartilage replacement and the introduction of new concept in medication by creating the cryogel like a controlled drug release system. The morphology of the cryogels, the interaction between the pva macromolecular chains and medicament has been studied by Scanning Electronic Microscopy. The gels swelling in physiologic ser have been monitored by gravimetric method in order to evidence the hydrophilic properties. The mechanical properties of the cryogels have been investigated by dynamic mechanical measurements. In conclusion, the biomaterial obtained provides good swelling properties, mechanical resistance and it is ideal for extended drug release implantable systems.

Abstract: The paper presents the effect of laser shock processing on stainless steel 316L corrosion resistance. The samples were laser welded and mechanical treated using a Nd:YAG laser with a 1064 nm wavelength, and two different pulse density: 900 pulse/cm² and 1600 pulse/cm². After the laser shock processing, the samples were subjected to a seawater solution for corrosion testing. The curves obtained were statistically modeled using Stern-Geary equation. One may observe that the corrosion speed of the LSP samples treated with 900 pulse/cm² is eight times higher than the corrosion speed of the LSP samples treated with 1600 pulse/cm².

Abstract: The objective of this research is to observe the influence of the sintering temperature on the wear testing for some steel samples elaborated by powder metallurgy technology. For obtaining the steels there were used iron powders and graphite powders. The powders were homogenized in a high energy ball mill Pulverisette 6, cold compacted and then sintered in a furnace. The sintering parameters are: the sintering temperature, T = (1050, 1100, 1150)°C and the maintaining time, t = 60 minutes. The influence of the sintering parameters on the samples wear behavior is studied using both a tribometer and a profilometer.

Abstract: A new composition of a dental cobalt alloy was proposed from the system CoCrMoTi, which are proposed for dental applications. Three content of titanium were used in commercial matrix of CoCrMo alloy in order to reveal the wear behavior of these alloys. The results showed that titanium alloying may improve wear behaviour by increasing the friction coefficient.

Abstract: Joint prosthesis involves the combination in the form of friction couplings of the different materials such as two metals, metal-polymer and polymer-ceramic. This paper aims to analyze the wear particles produced from the friction between two biomaterials: ultra hight molecular weight polyethylene ( uhmwpe ) and magnesium aluminosilicate ceramic. To obtain the wear particles using a tribometer cetr umt-2 type that can reproduce the wear phenomena of different biomaterials in different humidity conditions and at various speeds of movement. The tests were performed in dry and lubricated friction conditions using saline solution, the best imitating biological conditions. The movement is similar to the friction torques of the hip joint: a semicircular motion of the polymer piece on the circular surface of the ceramic piece. Movement speed chosen is 0.25 m/s. Wear particles obtained were isolated from biomaterial surfaces and studied using scanning electron microscope. The images obtained are analyzed, particle's dimensions are extracted and then imported into autocad can provide information about the shape, size and surface of the particles. In light of these facts, we can say the inflammatory risk of biomaterial particles. In conclusion, the biomaterial particles are very small and the inflammatory rick is reducing to minimum in lubricated conditions.