Volume 8 (2008): Issue 4 (December 2008)

Aim of this paper is evaluation of susceptibility of high-strength steel welded joints to hydrogen degradation and establishing of applicable mechanism of their hydrogen-enhanced cracking.

High-strength quenched and tempered steel grade S690Q and its welded joints have been used. Susceptibility to hydrogen degradation of steel and welded joints has been evaluated using monotonically increasing load. Slow strain rate test (SSRT) was carried out on round smooth specimens in air, and seawater under cathodic polarization. Elongation and reduction in area were choosen as measures of susceptibility to hydrogen embrittlement. Fractographic examinations with the use of scanning electron microscope (SEM) were performed to establish suitable mechanism of hydrogen-enhanced cracking of the welded joints.

Tested high-strength steel and its welded joints are susceptible to hydrogen embrittlement when evaluated with the use of SSRT. The loss of plasticity is higher for welded joints then for the base metal.

There is no possibility to perform direct observations of exact mechanism of hydrogen-assisted cracking so far. On the base of mechanical tests and fractographic observations it is likely to deduce which of nowadays models of hydrogen degradation and cracking is the most viable.

Tested steel and its welded joints could be safely utilized in marine constructions under cathodic protection provided that overprotection does not take place.

Hydrogen-enhanced localized plasticity (HELP) model is more applicable mechanism of hydrogen degradation than other for high-strength welded joints in seawater environment.

Degradation examinations of outer surface of low-emission steam boiler evaporator tubes are presented in the paper. Metallographic evaluation of scale morphology, its micro sites chemical composition analysis and distribution of elements on cross sections have been performed. Water-wall tubes were exposed in steam boiler for up to two years period. Common tubes made of 16Mo3 steel suffered sulfide and molten salts corrosions. Thermal sprayed tubes with the single layer of 70%Ni 30%Cr alloy show better corrosion resistance, but become also susceptible to sulfide corrosion due to presence of internal voids and cracks. Double layer Al₂O₃/Ni-30Cr coatings withstand corrosion attack for more than one year operation, then failed due to internal heterogeneity and cracks generation.

Influence of laser treatment at cryogenic conditions on surface microstructure after cavitation test of the SUPERSTON alloy are presented in this paper. The cavitation test was performed using the rotating disc facility in IPM PAN Gdansk. The kinetics of mass loss during the cavitation process was determined for casting and laser remelted specimens. Surface and cross-section microstructure of the SUPERSTON alloy after laser treatment and cavitation test was observed by optical and scanning electron microscope.

Photovoltaic technology is worldwide used to provide reliable and cost-effective electricity for industrial, commercial, residential and community applications. The average lifetime of PV modules can be expected to be more than 25 years. The disposal of PV systems will emerge as a problem, considering the still increasing production of PV modules. Recycling of such modules can be done at about the same cost level as its disposal. Recovering the pure silicon from damaged or end-of-life PV modules can lead to economical and environmental benefit. Chemical treatment conditions need to be precisely adjusted in order to achieve the required purity level of the recovered silicon. For crystalline silicon based PV systems, a series of etching processes has been carried out as follows: electric connectors (etching or removing), ARC and n-p junction etching. The chemistry of etching solutions was individually adjusted for the different silicon cell types. Efforts were taken in order to formulate a universal composition of etching solution.

The modern coatings used in arthroplasty for long term implants are reviewed. The phosphate coatings are the most popular technique to improve the bone-implant interfacial strength and promote the osseointegration. The plasma spraying, electrophoretic precipitation, powder metallurgy, ion beam sputtering, high velocity oxy-fuel (HVOF) combustion spraying, sol-gel technique, biomimetic deposition are mostly used to obtain the phosphate, usually hydroxyapatite coatings.

The composite coatings based on HA are proposed to improve biochemical and mechanical properties. The Ti, Ti alloys, titania, zirconia, zinc particles and glasses are suggested to strengthen the HA matrix, and some organic compounds and polymers to improve the biochemical behaviour.

Among another coatings, titania, zirconia, aluminia, carbon and organic, glass - ceramics and titania - silicate coatings are mostly proposed.