Abstract: Phase constituent morphology in microstructure of two-phase α+β titanium alloys is determined by conditions of thermomechanical processing consisting of sequential heat treatment and plastic deformation operations. Results of previous research indicate that particularly solution treatment preceding plastic deformation significantly changes α-phase morphology and determines hot plasticity of titanium alloys. In the paper thermomechanical processing composed of β solution treatment and following hot forging of Ti-6Al-4V titanium alloy was analysed. Development of martensite plates during heating up and hot deformation was evaluated. Microscopic examinations revealed that elongated and deformed α-phase grains were fragmented and transformed into globular ones. Significant influence of martensitic transformation on elongation coefficient of α-phase grains after plastic deformation was confirmed. Based on results of elevated temperature tensile tests it was established that α-phase morphology in examined two-phase α+β titanium alloy, developed in the thermomechanical processing, can enhance their hot plasticity – especially in the range of low strain rates.
Abstract: Shape memory effects, the course and characteristic temperatures of phase transitions and mechanical properties and surface properties of NiTi alloys strongly depend on the chemical composition, the production process used and the plastic working and thermomechanical treatment as well as surface treatment. The test alloy was obtained by vacuum metallurgy by melting the components in a graphite crucible and casting into a graphite ingot mould. In order to obtain the rods in the process of hot plastic working, hot forging was applied using a smith hammer and rotary hot forging on a swaging machine. The resulting rods were subjected to an appropriate heat treatment and thermo mechanical treatment to obtain, at room temperature, a parent phase structure B2.The paper presents the results of the research of NiTi rods after hot rotary forging. The phase composition of the samples of the tested alloy after different heat treatments were determined by X-ray powder diffraction technique. It was found that at room temperature, depending upon the processing the samples had a structure parent phase with a small amount of martensite. The courses of phase transitions and the changes of the temperature characteristic were determined on the basis of the recorded DSC curves. It was found that the test rate after aging in the temperature range of 400-500 °C transitions take place involving the rhombohedral R phase. The temperature ranges of shape recovery of samples after various heat treatments were determined by recording the recovery of the shape during heating, in tests performed according to the standard ASTM 2082-06.
Abstract: The paper presents results of structural studies of hot extruded NiTi shape memory alloy that is in the B2 phase at room temperature. Texture of the alloy was determined from the X-ray diffraction measurements. It was found that in result of 60 % sample reduction (at a cross-section of a bar formed by hot extrusion) weak axial texture - type <110>B2 was formed. The volume of the grains oriented in this way was approx. 20 %. Basing on metallographic observations it was also found that the size of the grains formed as a result of the thermomechanical treatment was uniform with the average area of 1700 μm2. This information is significant from the point of view of functional properties. Hot extruded alloy revealed presence of the reversible martensitic transformation. Its characteristic temperatures were slight higher than in as-cast alloy. Moreover, the extruded NiTi alloy showed 100 % of the shape recovery.
Abstract: Titanium foams are widely used as biomaterials and potentially as a twin skinned, sandwich, structures for aerospace structures, filter or a catalyst or catalysts carrier for chemical reactions. The porosity is particularly important for tissues ingrowth and vascularity. Open porosity is essential in the case of flow-on machines. The distribution and size of pores is significant to achieve a uniform material effort and ensure to receive an appropriate hydraulic properties.The aim of this study was to determine the effect of titanium particle size and the amount of porogen on the microstructure and the size of pore interconnections in titanium foams made using saccharose as the space holder material.The paper characterizes titanium foam, made from the Grade 1 Ti powders (Alfa Aesar) with a particle sizes of 0.150 mm and 0.044 mm (separately) and spherical particles of saccharose (Pfeifer & Langen) having an average size of 0.7 ÷ 0.9 mm, as a porogen. There was prepared a mixture of powders of the proposed porosity of 50, 60 and 70%. Summarizing 6 mixtures were prepared. After sintering there were received specimens having a diameter of 8 mm and a height of 5 mm. Microstructure analysis was performed using the microtomography Skyscan 1172 (Bruker microCT) and the CTAn software (Bruker microCT).The results indicate the uniform pore distribution and size of the interconnections allowing high permeability.
Abstract: The TiNiNb alloys with nominal composition containing 5at.% and 10at.% of niobium, substituted for nickel, were produced using a powder metallurgy. Alloys were produced from the initial powders of titanium, nickel and niobium with purity about 99.7%. Mixed powders were sintered at vacuum furnace at various sintering condition. Alloys showed the presence of the reversible martensitic transformation occurring between the B2 phase and the monoclinic martensite B19'. Apart from the presence of the transformable phases, also the non-transformable phase Ti2Ni was identified. Moreover, in sintered alloy (shorter sintering time), some amount of the niobium was stated. Increase of the niobium content also increased characteristic temperatures of the martensitic transformation.
Abstract: In general titanium alloys are associated with biomedical applications due to their unique properties such as: high biocompatibility, high strength to density ratio. They have been commonly used as a prosthetic material. However the microstructural development by heat treatment, directly correlated with the changes in mechanical properties of the material, allows us to consider these alloys as components of machines. One of the main properties of machine components are tribological properties. Knowledge of tribological properties of the machine elements allow us to determine the parts' viability and improve the functionality of the entire engineering system. Titanium alloys are characterized by the low wear resistance caused by chemical reactivity and easy formation of adhesion joints. Intensive adhesive wear of this material is associated with the strong degradation of the material surface. To determine the influence of microstructure on the tribological properties of titanium alloys, dry sliding wear test was performed. The materials for the investigations were five titanium alloys. The tribological test was performed with a load of 100 N for 2000 s on a 500 m distance. The microstructural observations were performed by light microscopy, in addition the wear mechanism was also investigated and for each sample the mechanism of wear was defined. For this type of tribological test a small proportion of adhesive wear was observed. The main mechanisms of wear were microgridding and microcutting. The increase of material hardness does not seem to impact on the increase of average friction coefficient of the samples. Increase of friction coefficient corresponds to the decrease of mass loss for the titanium alloys.
Abstract: The results of the investigations on five different titanium alloys were presented in this paper. Two two-phase α+β alloys (Ti-6Al-4V and Ti-6Al-2Sn-4Zr-6Mo) as well as two β alloys (Ti-10V-2Fe-3Al and Ti-3Al-8V-6Cr-4Mo-4Zr) were studied. Moreover, Ti-48Al-2Cr-2Nb intermetallic alloy (γ alloy) was also investigated. All investigated alloys were tested in compression on Gleeble thermomechanical simulator under various strain rate and temperature conditions. Metallographic observations of the microstructure of tested samples allowed determining thermomechanical conditions under which dynamic recrystallization or recovery processes occurred in the investigated alloys. The obtained results also showed the importance of the influence of strong exothermic effect resulting from deformation process on recovery and recrystallization processes in these alloys. The methodology of distinguishing subgrains formed during recovery process from the grains resulting from recrystallization was also presented in this study.
Abstract: The results of the investigation of the supersaturation temperature - in the range 800÷1050°C - influence on changes in the microstructure and hardness of the Ti24Nb4Zr8Sn alloy. The microstructure analysis was performed by means of the light microscope Axiovert 200MAT of the Zeiss Company. At the supersaturation temperature of 950°C examinations were performed by means of the scanning electron microscopy (SEM), while the occurring phases were identified by using X-ray phase analysis method. Tin precipitates of a high dispersion were found in the phase β matrix. Along with the decreasing cooling rate of the alloy, from a temperature of 950°C, none essential changes in the microstructure were noticed (only a small hardness decrease). Hardness measurements were carried out by means of the Vickers apparatus, type HP0 250. It was shown that within the tested supersaturation temperatures the hardness is within a narrow range 216÷246 HV, while the average diameter of a flat grain of the primary β phase increases more than twice.The obtained results will be used at elaborating ageing parameters of the Ti24Nb4Zr8Sn alloy. In future, they can be also useful at designing chemical compositions, microstructures and heat treatment technologies of new, single-phase alloys on the titanium matrix.
Abstract: The aim of the study was to obtain zirconium and calcium doped zirconium coatings using sol-gel methodology and their further modification with electrophoretically deposited hydroxyapatite. Both systems phase composition was investigated using Raman spectroscopy. Their morphology and composition was studied using scanning electron microscope (SEM) with X-ray microanalysis (EDS), while their topography was observed using atomic force microscope (AFM). The osseointegrative properties of both coatings were investigated using in vitro Simulated Body Fluid (SBF) test. The resulting systems were studied using the same methods that were applied to the two coatings.