Solid State Phenomena Vol. 183

Abstract: The primary limitation of weldability of high strength low alloy steel is susceptibility to cold cracking. The important reason of the formation of cold cracks, besides forming brittle structure and residual stresses, is the presence of diffusible hydrogen in welded joint. The most effective methods reducing the susceptibility to cold cracking are connected with decreasing the amount of potential hydrogen. This process may be carried out in technological (drying welding filler materials, preheating components) or in a metallurgical way (filler metals with austenitic structure, adding rare-earths elements to filler metals as traps for hydrogen atoms in steel). The possibility to minimize the amount of diffusible hydrogen by changing the welding parameters seems to be particularly interesting. The article presents the results of a literature survey and preliminary tests which set out effects of welding conditions on the amount of diffusible hydrogen in deposited metal. Experiments were conducted by using rutile coated electrodes which generate high contents of diffusible hydrogen in deposited metal. The amount of diffusible hydrogen was determined by a glycerin test. Eleven factors were considered: the electrode angle, the grinding of sample, the preheat temperature, the polarity of welding current, the welding current, the welding – cooling time, the electrode usage, the time of welding, the thickness of specimen, the welding – measurement time and thickness of electrode coating. All factors were optimized using a Plackett-Burman design to get the most relevant variables. The results of the preliminary tests indicate that appropriate choice of welding parameters may considerably reduce diffusible hydrogen in deposited metal. However, the range of parameters is limited by the necessity of providing stability of the welding process and obtaining required properties of the welded joint.

Abstract: This paper presents investigation of cavitation erosion resistance of nitrided austenitic stainless steel X5CrNi18-10. The diffusion layers were produced by using different parameters of reactive atmosphere (N₂:H₂). The microstructure, chemical composition and phase identification of the modified layer were examined using scanning electron microscopy, glow-discharge optical emission spectrometer and X-ray diffractometry, respectively. Cavitation erosion resistance of produced surface layers was investigated in a rotating disc facility. As a property characterizing the cavitation erosion resistance of manufactured surface layers were proposed incubation period and mass loss after 330 min of cavitation test. It was found that cavitation erosion resistance of modified surface layers is lower than reference material (not treated X5CrNi18-10 stainless steel).

Abstract: In this paper, the results are presented of the ultrasonic investigations of hydrogen degradation of 09G2S carbon steel. Samples of the steel were hydrogen charged with simultaneous registration of the ultrasonic signal. The results of ultrasonic investigations were verified by Light Microscopy (LM), Scanning Electron Microscopy (SEM) and X-ray microanalysis technique (EDS). It was shown that the in-situ ultrasonic flaw detection can be used to monitor the early stages of hydrogen degradation, i.e. the formation of microcracks caused by hydrogen trapping at nonmetallic inclusions and hydrogen blistering.

Abstract: The titanium and its alloys can be subjected to surface treatment, including laser treatment. In this work a new laser treatment at cryogenic conditions of Ti6Al4V alloy has been described. The work has been aimed at establishing whether such surface treatment could be suitable for implants working under wear in biological corrosive environment. The remelting has been made with the use of CO₂ continuous work laser at laser power between 3 and 6 kW, at scan rate 0.5 and 1 m/s. The microstructure, surface topography, hardness, microhardness and wear linear rate and mass loss under tribological tests made in Ringer`s solution have been made. The results have shown that despite the surface cracking the tribological properties in simulated body fluid have been substantially improved.

Abstract: The main objective of here presented research is a design the scaffold/porous titanium (Ti) alloy based composite material demonstrating better biocompatibility, longer lifetime and bioactivity behaviour for load-bearing implants. The development of such material is proposed by making a number of consecutive tasks. Modelling the mechanical, biomechanical and biological behavior of porous titanium structure and an elaboration of results is performed by mathematical methods, including FEM and fuzzy logic. The development of selected Ti-13Zr-Nb alloy with designed porosity and no harmful effects is made by powder metallurgy (PM) with and without space holders, and by rapid prototyping with an use of selective laser melting (SLM). The development of an oxidation technology resulting in high corrosion resistance and bioactivity is carried out by electrochemical oxidation, gaseous oxidation and chemical oxidation, and their combination. The HA depositon is made by electrochemical and chemical (alternate immersion) methods. The core material is designed as a combination of natural polymer and bioceramics in order to allow slow dissolution followed by stepwise growth of bone tissue and angiogenesis, preventing local inflammation processes, and sustaining the mechanical strength close to that of non-porous material.

Abstract: The surface layers resulting from prolonged exposure to the indoor environment and the bulk material of metal artifacts from the collection of National Museum in Gdansk are studied by means of spectroscopic techniques. The composition of the surface layers of the forged iron box lid covered with polychrome (XVI c.), and of the bronze female nude sculpture (antiquity) is obtained from the XRF and µ-Raman spectra. The elemental composition is confirmed by the LIP (Laser Induced Plasma) spectroscopic measurements. The quasi-nondestructive LIP technique applied for stratigraphic sampling performed with an accuracy of ca 2 µm across the multilayer surface coverage reveals such elements as C, Ba and Na in the uppermost layer. From coincidence of the XRF, Raman and LIP data the presence of surface contaminant CaCO₃, the corrosion product FeO(OH) and patina Cu₂ (OH)₃Cl are concluded. It is shown that the complementary spectroscopic analysis allows for the in-depth study of the environmental impact on historical objects and delivers indications for the appropriate strategy of the planned conservation activities. Moreover, from the data collected from the technologies applied in the past, origin, provenance and routing of the artifacts can be concluded.

Abstract: Great interest of the laser beam welding in industry is a new theoretical task, making planning the welding procedure specification and the quality control of welded joints easier. Estimating and calculating the dimensions of a weld pool and temperature distribution near weld mainly concern heat source modelling. In the presented work calculations of welding pool shape and thermal field for cylindrical-powered-normally model of heat source have been presented. Parameters of the model of heat source and weld pool geometry were determined using analytical-numerical calculations. The results of numerical calculations were compared with the experimental data for butt joint made by CO₂ laser beam. Comparable results have been observed. Practical recommendations for assumptions of model parameters - the flux density energy distribution of the heat source in case of calculations of the thermal field in the vicinity of a weld pool are given.

Abstract: Hydroquinone derivatives are studied as inhibitors of microbiological corrosion and hydrogen absorption by mild steel in water salt media that supports development of sulfate reducing bacteria (SRB). The chosen composition of the media is close to sea water containing biogenic H2S. Н2S content, bacterial titer in corrosive media, its pH, Redox potential Eh, and φ of steel together with the quantity of hydrogen absorbed by surface steel sub-layers, were measured. Protective action against corrosion achieved by the best compounds studied, reached the values of 65…84%, while against hydrogen absorption by steel samples − 60…72%. The presence of the studied derivatives of hydroquinone at concentration C= 5 mMoldm–3 resulted in the decrease of SRB cell count at the rate of 48…84%, the suppression rate being at the values of 29…57%.