EVOLUTION OF MICROSTRUCTURE OF LASER SURFACE ALLOYING OF γ TiAi ALLOY WITH NITROGEN

Laser surface alloying of γ TiAl alloy with nitrogen was studied under the constant protective nitrogen current (20l /min). The experimental results shown that the surface multi layers formed with experimental parameters could be up to 600μm depth; it consists of TiN,Ti 2AlN,α 2 and γ phases, without AlN, and the irregular coarse continuous “flow” line,dendrite,needle and granular nitrides disperse on the fine dendrite casting α 2 and γ phases substrate. The microstructure and compositions in the nitiding layer were determined and analyzed by SEM and EPMA and the mechanism for the formation of microstructure in the nitriding layer was also discussed.

Optimizing Domain Distribution of Grain Oriented Silicon Steel by Using Antimony as the Laser Surface Alloying Element

For reducing the core loss of grain oriented silicon steel and improving its aging property, a new method, the LLSA by using Sb as the laser surface alloying element, was investigated, and at proper technique conditions rather good result was obtained.

Influence of yttrium on laser surface alloying organization of 40Cr steel

In order to improve the performance of the metal rollers, Mo＋Y2O3 alloy powders were used to coat uniformly on the surface of 40Cr steel roller substrates for the laser surface alloying treatment by a CO2 laser, The results showed that many good consequences were ob- tained after adding the rare earth oxide Y2O3. The crystal grains of the alloy layer were significantly refined. The boundary of crystal grains was strengthened. The unifomaity and density of the microstructure were increased. The hardness and wearing resistance of the alloy layer were considerably improved. The valence electron structure analysis of the alloy layer was made by the empirical electron theory of solids and molecules （EET）. The calculated results demonstrated that Y should be mixed in the first stage and Fe should be in the eighteenth hybrid bands. The analyzed outcomes illustrated that the electron theory of the solid solution shows the strengthening effect on the alloying layer, which has enhanced bond and confirrned the experimental results.

Laser Surface Alloying of Low Carbon Steel Using High-entropy Alloy Precursors

The Al0. 5CoCrCuFeNi high-entropy alloy powders with simple face-centered-cubic （FCC） solid solution structure were introduced into the surface layer of a low carbon steel during laser surface alloying. A high performance surface layer with extremely fine martensite as the dominant phase was obtained, resulting in a great improvement in microhardness, wear resistance, and corrosion resistance. The great enhancement of microhardness and wear resistance of the laser alloyed layer is mainly due to the formation of extremely fine martensite hard phase, the solid solution strengthening of the alloying e!.ements in supersaturated a-Fe solid solution, and the existence of size effect and strain effect under rapid solidification. The enhancement of corrosion resistance is due to the alloying of Al, Co, Ni, Cr and Cu in the laser alloyed layer.

Cavitation erosion behavior of WC coatings on CrNiMo stainless steel by laser alloying

The WC powder was precoated on the surface of CrNiMo stainless steel and then made into an alloying layer by using the laser alloying technique. Phases in the layers were investigated by X-ray diffraction （XRD） analysis and surface morphologies after cavitation erosion were observed with the help of scanning electron microscopy （SEM）. The cavitation erosion behavior of the CrNiMo stainless steel and WC laser alloying layer in distilled water was tested with the help of ultrasonic vibration cavitation erosion equipment. The results showed that the thickness of the laser alloying layer was about 0.13 mm. The layer had a dense microstructure, metallurgically bonded to the substrate, and no crack had been found. The cavitation erosion mass loss rate of the laser alloying layer was only 2/5 that of the CrNiMo stainless steel. The layer had better cavitation resistance properties because of its metallurgical combination and the strengthening effects of the precipitate phases.

Corrosion Resistance of AZ91 Magnesium Alloy after Laser Remelting Treatment

The main objective of the study was the modification of the surface layer of magnesium alloy by the COlaser. The studied material was the commercial AZ91 magnesium alloy. The effectiveness of the alternations caused by the remelting process was verified on the basis of microscopic observation and corrosion investigations, i e, recording of potentiodynamic polarization curves, electrochemical noise measurements and hydrogen evolution rate measurements. For the adopted range of the treatment parameters, favourable changes were observed in the surface layer such as the refinement of structure and more uniform arrangement of individual phases. As a consequence of those favourable structural changes the improvement of the corrosion resistance of the alloy was achieved in comparison to its non-remelted equivalent. For the treated material corrosion rates expressed as corrosion current densities were at least three times lower than the appropriate values for the untreated alloy comparing them for the same period of samples immersion in the test solution. The obtained results have confirmed the effectiveness of the applied surface treatment resulting in favourable changes in the structure and corrosion properties of the AZ91 magnesium alloy.

Formation of TiN Grid on NiTi by Laser Gas Nitriding for Improving Wear Resistance in Hanks' Solution

Laser gas nitriding （LGN） is a common surface modification method to enhance the wear resistance of titanium （Ti） alloys, which are known to have poor tribological properties. In the present study, a titanium nitride （TIN） grid network was fabricated on the surface of nickel titanium （NiTi） by LGN. The laser processing parameters were selected to achieve nitriding without surface melting and hence to＇maintain a smooth surface finish. The characteristics of the grid-nitrided samples were investigated by scanningelectron microscopy, X-ray diffractometry, optical microscopy, 2-D profilometry, contact angle measurements and nanoindentation. The wear resistance of the nitrided samples was evaluated using reciprocating wear test against ultra-high-molecular-weight polyethylene （UHMWPE） in Hanks＇ solution. The results indicate that the wear rates of the grid-nitrided samples and the UHMWPE counter-body in the wear pair are both significantly reduced. The decrease in wear rates can be attributed to the combination of a hard TiN grid and a soft NiTi substrate. In Hanks＇ solution, the higher hydrophilicity of the nitrided samples also contributes to the better performance in wear test against hydrophobic UHMWPE.