EFFECTS OF Nb/Ti+ Nb MICRO ALLOYING ON 900℃ TENSILE PROPERTIES OF ALLOYGH652

Theeffectsof Nband Ti+ Nb microalloyingon mechanicalpropertiesand rupturelifeunder900 ℃ tensiletest on alloy GH652 were studied. Among theoriginalalloy GH652 and its Nb/ Ti+ Nb microalloyed alloys, the Ti+ Nb microalloyed alloy exhibited optimum com bined900℃ tensilestrength and plasticity and longer 900℃ 49 MPa prolonged tensile rup turelife as well. The role of refractory alloying elementscould be effectively brought intoplay with highertemperaturesolution treatment. Coordination strengthening of Matrix andgrain boundary wasthekeyfactoroflifetimeextension andthe mobilityof dislocationsinthematrix wasresponsableforthe plasticity ofthe micro alloyedsamples.

Microstructure and Properties of ZL101 Alloy Affected by Substrate Movement Speed of a Novel Semisolid Continuous Micro Fused-Casting for Metal Process

A novel semisolid continuous Micro Fused-Casting additive manufacturing technology for producing a ZL101 alloy strip was developed, Micro Fused-Casting means that the semisolid metal slurry was pressed out from the outlet of bottom of crucible to the movable plate. The degree of sub-cooling was easily provided by movement of substrate in the micro fused-casting area. Under the aid of 3 D manufacturing software, the ZL101 alloy strip was solidified and formed layer by layer. The microstructure and properties of ZL101 semisolid slurry were improved by the cooling conditions. The results showed that the ZL101 alloy strip samples fabricated by Micro Fused-Casting had uniform structures and good performances with the substrate movement speed at 20 mm/s and the temperature at 590 ℃, the ultimate tensile strength and elongation of the ZL101 alloy strip reached 242.59 MPa and 7.71%, while the average Vickers hardness was 82.55 HV.

INFLUENCES OF MICRO-ALLOY AND HEAT-TREATMENT PROCEDURE ON THE HARDENING OF DJ108TI ALLOY

The influences of micro alloy and heat treatment procedure on the hardening of DJ108Ti alloy, which is based on the electrolytic Al Si(2 05%) Ti(0 25%) Fe(0 30%) multi component alloy, have been investigated. The results indicate that the micro alloy based on the multi component alloy makes α Al dendrites in DJ108Ti alloy refined; that the improved heat treatment procedure makes the eutectic Si phases granulated , the Fe phase refined, and the strengthening phases of Mg2Si and Al2Cu fully precipitated. The micro alloy and the heat treatment procedure harden DJ108Ti alloy and benefit the abrasion resistance of the alloy

Fabrication of Micro/Nano-textured Titanium Alloy Implant Surface and Its Infl uence on Hydroxyapatite Coatings

We put forward a protocolcombining laser treatment and acid etching to obtain multiscale micro/nano-texture surfaces of titanium alloy implant.Firstly,the operationalparameters of the laser were optimized to obtain an optimum current.Secondly,the laser with the optimum operationalparameters was used to fabricate micro pits.Thirdly,multiple acid etching was used to clean the clinkers of micro pits and generate submicron and nanoscale structures.Finally,the bioactivity of the samples was measured in a simulated body fluid.The results showed that the micropits with a diameter of 150 μm and depth of 50 μm were built successfully with the optimized working current of 13 A.In addition,submicron and nanoscale structures,with 0.5-2 μm microgrooves and 10-20 nm nanopits,were superimposed on micro pits surface by multiple acid etching.There was thick and dense HA coating only observed on the multiscale micro/nano-textured surface compared with polished and micro-textured surface.This indicated that the multiscale micro/nano-texture surface showed better ability toward HA formation,which increased the bioactivity of implants.

Carbide and Nitride Precipitation in High Temperature TensiledSpecimens and Hot Ductility of Nb-and Ti-ContainingSteel CC Slabs

Hot ductility of the Nb- and Ti-containing line-pipe steel CC slab specimens were measured under the sirain rate of 1 x 10-3/s. Three types of precipitates were found in the fractured specimens. One was the block-shaped coarse TiN particles precipitated at high temperature. Another type was the fine dynamic precipitation products precipitated at 950～900℃ which caused remarkable ductility reduction of the steel. The third type was the co-existed precipitates formed by fine Nb precipitates nucleating and growing on TiN paricles. Compared with Nb-containing steel which contains no Ti, there was no ductility drop for Nb- and Ti-containing steel at temperature between 850℃ and Ar3 and, the γ→α transformation inside the grain matrixes proceeded faster, which both improved the ductility of the steel in the low ductility temperature Region Ⅲ.

Strengthening Mechanisms for Ti-and Nb-Ti-micro-alloyed High-strength Steels

The strengthening mechanisms of hot-rolled steels micro alloyed with Ti （ST-TQS00） and Nh Ti （NT TQ500） were investigated by examining the microstructures of steels using optical microscope （OM）, scanning elec tron microscope （SEM） and transmission electron microscope （TEM）. The results revealed ahnost no differences in the solute solution strengthening and fine grained strengthcning of the two steels, whereas the contributions of pre cipitation strengthening and dislocation strengthening were different for ST-TQ500 and NT-TQ500. The measured precipitation strengthening effect of ST-TQ500 was 88 MPa higher than that of NT-TQ500： this difference was pri marily attributed to the stronger precipitation effect of thc Ti-containing nanoscale particles. The dislocation strengthening effect of ST TQ500 was approximately 80 MPa lower than that of NT-TQ500. This is tbought to be related to differences in deformation behavior during the finishing rolling stage; the inhibition of dynamic recrystallization from Nb in NT-TQ500 （Nb-Ti） may lead to higher density of dislocations in the microstructure.

Microstructure and Tribological Behavior of a TiO_2/hBN Composite Ceramic Coating Formed via Micro-arc Oxidation of Ti–6Al–4V Alloy

A composite coating containing hexagonal boron nitride（hBN） particles and titanium oxide（TiO_2） was formed on the surface of Ti-6Al-4V alloy via micro-arc oxidation（MAO）. The effect of quantity of the hBN-particles added into electrolyte on microstructure, composition, and wear behavior of the resulting composite coatings was investigated. Microstructure, phase composition, and tribological behavior of the resulting MAO coatings were evaluated via scanning electron microscopy, X-ray diffraction, and ball-on-disc abrasive tests. The results reveal that the TiO_2/hBN composite coating consisting of rutile TiO_2, anatase TiO_2, and an hBN phase was less porous than particle-free coating. Furthermore, the presence of hBN particles in the MAO coating produced an improved anti-friction property. The composite coating produced in the electrolyte containing 2 g/L of hBN particles exhibited the best wear resistance.The outer loose layer of the MAO coatings was removed by a mechanical polishing process, which led to a significant improvement in the wear resistance and anti-friction properties of the MAO coatings and highlighted an essential lubricating role of hBN particles in the composite coatings. However, wear mechanism of the MAO coatings was not relevant to the presence of hBN particles, where fatigue wear dominated the anti-fraction properties of the MAO coatings with and without hBN particles.