Microstructure of Laser Processed T10 Carbon Tool Steel

The microstructure of the laser melted 1.0%C tool steel have been investigated.The region affected by the laser can be subdivided into 3 zones,which consist of a melted region at the surface,a zone with solid state transformation and the area adjacent to the unaffected substrate where cementite is slightly dissolved.The melted zone possessed a cellular growth morphology consisting of austenite and martensite.The carbon content of the austenite was measured to be over 1 wt-%.A great deal of retained austenite and twinned martensite were found in the first two zones(the melted and solid transformed).

区熔法生长近化学计量比铌酸锂晶体

The congruently melting composition of Lithium Niobate(LN) is 48.6mol% Li 2O,rather than stoichiometric 50mol%Li 2O.By means of conventional Czochralski(CZ) method,it is easy to grow the congruent LN crystal with high quality,but difficult to grow the stoichiometric LN crystal with homogeneous composition. In contrast to CZ method,Melting Zone(MZ) method makes use of the segregation of solute,and is likely to grow homogeneous crystal.By MZ method,we have grown near stoichiometric LN crystal (Li%mol=49.5%) from stoichiometric LN raw material. The difference between the raw material and the crystal is due to the volatilization loss of Lithium at the growing temperature.With 50.5mol%Li 2O LN raw material,stoichiometric LN crystal could be grown. Li rich LN solvent zone preplaced in the melting zone makes the crystal much more homogeneous than that without the solvent zone.The preplaced Li rich zone heightens the starting [Li] concentration of the liquid phase,so that the initial [Li] concentration of LN crystal is close to the stable value,and the process of stabilization is shortened.

Thermoelectric performance of p-type zone-melted Se-doped Bi_(0.5)Sb_(1.5)Te_3 alloys

For zone-melted （ZM） bismuth telluride-based alloys, which are widely commercially available for solidstate cooling and low-temperature power generation around room temperature, introducing point defects is the chief approach to improve their thermoelectric performance. Herein, we report the multiple effects of Se doping on thermoelectric performance of p-type Bi0.5Sb1,5Te3-xSex ＋ 3 wt% Te ZM ingots, which increases carrier concentration, reduces lattice thermal conductivity and deteriorates the carrier mobility. As a result, the peak figure of merit （ZT） is shifted to a higher temperature and a high ZT 1.2 at 350 K is obtained, due to the reduced thermal conductivity and suppressed intrinsic conduction. Further, decreasing Sb content is followed to optimize the room temperature performance and a ZT - 1.1 at 300 K is obtained. These results are significant for designing and optimizing the thermoelectric performance of commercial Bi0.5Sb1.5Te3＋ 3 wt% Te ZM alloys.

Mid-temperature thermoelectric performance of zone-melted Sb_(2)(Te,Se)_(3) alloys near phase transition boundary

(Bi,Sb)_(2)(Te,Se)_(3) alloys are widely used commercial thermoelectric(TE)materials for solid-state refrigeration around room temperature.The composition-induced structural phase transition could be realized by varying the compositions in these alloys,which may largely alter the electronic structure and phonon dispersion.Among them,the Se-alloyed Sb_(2)Te_(3) accompanied with structural transition is seldom reported.Herein,the interrelations of Se-alloying induced changes in structural phase transition,band structure and TE properties of p-type zone-melted Sb_(2)Te_(3-x)Se_(x)(x=1.5-2.4)alloys near phase transition boundary are systematically investigated.The results demonstrate that Sb_(2)Te_(3-x)Se_(x) shows a structural transition from a rhombohedral phase to mixed structure at x=2.0.The carrier concentration and bandgap at room temperature of Sb_(2)Te_(3)-xSex(x=1.5-2.4)constantly decrease with increasing Se contents x.The zT peak of the Sb_(2)TeSe_(2) matrix is improved and shifted to higher temperature by optimizing carrier concentration via Ag doping.A maximum zT of~0.4 is obtained at 680 K in Sb_(1.97)Ag_(0.03)TeSe_(2) alloy,about 100% enhancement compared with the undoped sample.

Unveiling the dynamic instability mechanism of microstructure transformation in faceted oxide eutectic composite ceramics

Microstructure control is a great challenge in the high-temperature gradient directional solidification of eutectic composite ceramics due to the complex solidification behavior.Herein,the microstructure trans-formation of faceted Al_(2)O_(3)/Er_(3)Al_(5)O_(12) thermal emission eutectic composite ceramics is explored over wide ranges of compositions(13.5 mol%-22.5 mol%Er_(2)O_(3))and solidification rates(2-200μm/s).Entirely cou-pled eutectics with primary phases suppressed are fabricated and the coupled zone is broadened in a wide range of 15.5 mol%-22.5 mol%Er_(2)O_(3) at low solidification rates.The competitive growth between eutectic and dendrite is evaluated on the basis of the maximum interface temperature criterion.In ad-dition,the mechanisms of irregular eutectic spacing selection and adjustment under different solidifi-cation rates are revealed based on Magnin-Kurz model.A successful prediction of lamellar to rod-like eutectics is achieved associated with the dynamic instability of lamellar eutectic and the corresponding enlarged coexistence region is mapped based on the interface undercooling.According to the well mi-crostructure tailoring,the flexural strength of Al_(2)O_(3)/Er_(3)Al_(5)O_(12) eutectic composite ceramics has improved from 508 MPa up to 1800 MPa due to the refined eutectic spacing with low fluctuation.The eutectic composite ceramics show strong selective optical absorption and the intensity increases with the refin-ing microstructure.The as-designed Al_(2)O_(3)/Er_(3)Al_(5)O_(12) composites with microstructural tailoring have great potential as integrations of structural and functional materials.

Improving Weld Quality by Arc-Excited Ultrasonic Treatment

Ultrasonic treatment of the solidifying metal is a promising method for improving the quality of fusion welding. A method to combine the ultrasonic waves to the welding process using arc excited ultrasonic emission, called arc ultrasonic, was high frequency modulation of the arc plasma. The effects of arc ultrasonic on the weld including the fusion zone, the partially melted zone and the heat affected zone are described. The arc ultrasonic energy changes the weld microstructure. In the fusion zone, the primary dendrite arm spacing decreases significantly and more acicular ferrite appears. In the partially melted zone, a large amount of fine grains appear. In the heat affected zone, the width of the tempered zone increases with increasing modulation frequency and the microstructure is refined. The results show that arc ultrasonic is a new and effective way for improving weld quality.

Softening and Melting Behavior of Ferrous Burden under Simulated Oxygen Blast Furnace Condition

The softening and melting behavior of sinter, pellet and mixed burden was researched through high tem- perature reaction tests under load simulating traditional blast furnace （T-BF） and oxygen blast furnace （OBF） condi- tions. The results indicated that compared with T-BF, the softening zone of sinter and pellet became wide, but the melting zone became narrow in OBF. The permeabilities of both sinter and pellet were improved in OBF. Under the condition of OBF, the temperature of softening zone of mixed burden was increased by 63 K, but the temperature of melting zone was decreased by 76 K. Therefore, the permeability of material layer was significantly improved. This was mainly caused by the change of the melting behavior of pellet. In addition, the quality Of dripping iron in OBF was much better than that of T-BF.

Distribution control and formation mechanism of gas inclusions in directionally solidified Al2O3-Er3Al5O12-ZrO2 ternary eutectic ceramic by laser floating zone melting

Distribution control and formation mechanism of gas inclusions formed in directionally solidified Al2O3-Er3Al5O12-ZrO2 eutectic ceramic rods are explored during laser floating zone melting. In atmospheric environment, highly-dense bubble-free eutectic rods are well fabricated at low solidification rate(<25μm/s). Gas inclusions form intermittently when the solidification rate is in the range of 25-50 μm/s,but produce continuously at higher solidification rates(100-200 μm/s). The gas inclusions exhibit an elongated finger-like pattern along the growth direction, which of the maximum value of diameter first increases and then decreases with increasing the solidification rate. Meanwhile, the volume fraction of gas inclusions increased gradually with the solidification rate. Based on the effect of surface tension gradient, heterogeneous nucleation of gas bubbles is evaluated to be the primary formation mechanism of gas inclusions.

Phase growth patterns for Al_(2)O_(3)/GdAlO_(3)eutectics over wide ranges of compositions and solidification rates

Phase selection and growth characteristics of directionally solidified Al_(2)O_(3)/GdAlO_3(GAP)faceted eutectic ce ramics are investigated over wide ranges of compositions and solidification rates to explore the eutectic coupled zone.Through the obse rvation of the quenched solid-liquid interface,the competitive growth of primary faceted Al_(2)O_(3)phase,prima ry non-faceted GAP phase and Al_(2)O_(3)/GAP eutectic with diffe rent morphologies is detected.Microstructure transitions from wholly eutectic to primary Al_(2)O_(3)(GAP)dendrite plus eutectic and then to wholly eutectic are found in Al_(2)O_(3)-2 O mol%Gd_(2)O_(3)hypoeutectic(Al_(2)O_(3)-26 mol%Gd_(2)O_(3)hypereutectic)ceramics with the increase of solidification rate.The dendrite growth of faceted Al_(2)O_(3)and non-faceted GAP phases are well predicted by KGT model,which have introduced appro p riate dimensionless supersaturationΩto characterize the anisotropic growth of dendrites.Based on the maximum interface temperature criterion,the competitive growth of primary phase and eutectic is analyzed theoretically and the predicted coupled zone of Al_(2)O_(3)/GAP eutectic ceramics is in good agreement with the experimental results.Besides,the influence of microstructure with these different morphologies on the flexural strength of Al_(2)O_(3)/GAP eutectic ceramics is studied.

Microstructure and mechanical properties of hybrid fabricated 1Cr12Ni2WMoVNb steel by laser melting deposition

Laser melting deposition was carried out to deposit a 1Cr12Ni2WMoVNb steel bar on a wrought bar of same material. Room-temperature tensile properties of the hybrid fabricated 1Cr12Ni2WMoVNb steel sample were evaluated, and microstructure, fracture surface morphology, and hardness profile were analyzed by an optical microscope （OM）, a scanning electron microscope （SEM）, and a hardness tester. Results show that the hybrid fabricated 1Cr12Ni2WMoVNb steel sample consists of laser deposited zone, wrought substrate zone, and heat affected zone （HAZ） of the wrought substrate. The laser deposited zone has coarse columnar prior austenite grains and fine well-aligned dendritic structure, while the HAZ of the wrought substrate has equiaxed prior austenite grains which are notably finer than those in the wrought substrate zone. Besides, austenitic transformation mechanism of the HAZ of the wrought substrate is different from that of the laser deposited zone during the reheating period of the laser deposition, which determines the different prior austenite grain morphologies of the two zones. Microhardness values of both the laser deposited zone and the HAZ of the wrought substrate are higher than that of the wrought substrate zone. Tensile properties of the hybrid fabricated 1Cr12Ni2WMoVNb steel sample are comparable to those of the wrought bar, and fracture occurs in the wrought substrate zone during the tensile test.