The biomaterials most widely used for hard tissue implants (in orthopaedics, dental implants, and skull bones) are Ti-based biomaterials and Ti coated with hydroxiapatite (HAP). Because metallic biomaterials have some disadvantages as reported previously (mainly due to the difference between the mechanical characteristics of the human bone and the metallic implant), biocomposites have become an interesting solution to improve the hard tissue implants for the human body. This article presents the experimental results concerning the processing of HAP/Ti biocomposites by powder metallurgy technology. The initial powder mixture consists of HAP powder particles (<200 nm) reinforced with 100 μm titanium particles in the ratio 3:1 (wt%). Two different sintering routes are used: spark plasma sintering (SPS) at (1000-1100) • C for 10 or 20 min and two-step sintering (TSS) with the first step at 900 • C/1 min, followed by the second step at 800 • C for 300, 600, 900 or 1200 min. The ball-on-disc dry wear tests are developed using, as a moving counterpiece, DIN 100Cr6 tool steel balls (6 mm diameter; Ra < 3.2 μm; HRc 60-64; density >7.6 g/cm 3 ). The tribological behaviour of the processed biocomposites is appreciated on the basis of the coefficient of friction and wear rate, corroborated with the wear track depth. The final remarks of this article underline the potential use of SPS technology to obtain HAP/Ti biocomposites with comparable wear properties as similar materials processed by more complex technologies. Also, TSS allows processing HAP/Ti materials comparable with the SPS-ed ones from the point of view of the wear behaviour, except for the dwell time of the second step, which is critical for the wear behaviour.

Heated tool and electrofusion welding are the most used joining processes of higher than 2 mm thick polymer pipes. The two welding processes have different heating-cooling cycles and they produce different influences on the properties of the polymers. Exploitation of polymer pipes for water and gas distribution revealed ageing behaviour of the material in the welding area. The modification of the behaviour depends on the base material, on the applied welding process and on the used parameters. Thermal analysis can be used as tool to reveal and to evaluate the modification of the physical and mechanical properties. Such knowledge is important when prediction of the in use life is necessary to be predicted. Experimental programme was applied to HDPE 100 and HDPE 80, both welded using heated tool and electrofusion processes and different sets of parameters (factorial experiment principles were used to establish the welding parameters). Plasticity characteristics of the welds material, as elongation and relaxation modulus, were determined by using thermal analysis. Burst stress test, applied to the pipe, was considered. It has been observed important rate of the heating process of the surface in contact with the heater. The DSC analysis revealed a decreasing of the elongation with about 12% and decreasing of the relaxation modulus with amount up to 14%, for the material located at the interface between pipe and the heater. At 0.5 mm from the interface it was revealed an intensity of the modification up to half of the values recorded for the interface. That was explained on the poor thermal conductivity specific to the both materials. By using DSC thermal analysis it has been revealed that the polyethylene has high rate crystallization during welding cycle, after the heating to the viscous state. Such crystallization, together with potential non-uniformity of the heating provides modifications in the geometrical characteristics of the weld. For high energy input, the material experience large quantity of fluid material with important plastic distortion. That means high possibility to reject material during pressing step of the welding cycle. 10% increasing of the temperature, for the same heating pressure, involves 5-8% increasing of the dimensions of the fluid ring in the interface. About 10% difference between the relaxation modulus of the heated and non-heated HDPE and that means local ageing transformation of the HDPE. The material becomes more fragile than before the welding process.

The paper deals with the influence of coatings on the tool life of the different shapes of taps in a thread cutting process. The PVD procedure was employed in order to apply a TiAlN coating on the various type of taps.The influence of the tap geometry was very important and affected significantly the tool life measured in the number of holes tapped. The wear pattern for each type of tap was analyzed as well. The TiAlN coatings promote the formation of protective alumina films composed of amorphous-crystalline structures improving the tribological behavior of the coated tools.

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The nanostructured biocomposites with hydroxyapatite (HAP) matrix reinforced by titanium (Ti), processed by two steps sintering (TSS) route in argon atmosphere, provide excellent wear behaviour when they are elaborated in specific sintering parameters. The wear tests, developed in steel ball-on-disc dry conditions, show low wear rates about 2x10-4 [mm3/Nm] when the biocomposites are processed at 750...8000oC for 450...600 min. in comparison with high wear rates 7x10-4 [mm3/Nm] in 700...7500oC for 300 min. as TSS parameters. The X-ray diffraction (XRD) and scanning electron microscopy (SEM) analysis outline the structural features that explain this wear behaviour.