Yongfeng Liang

Cold rolled Fe-6.5 wt. % Si alloy foils with high magnetic induction

Fe-6.5 wt. % Si alloy foils with 95 mm in width and 0.30 mm in thickness were successfully fabricated by cold rolling process. Excellent magnetic properties (Hc = 20.4 A/m, µm = 22 200, and Bs = 1.69 T) were obtained after annealing at the temperature of 1273 K for 1.5 h. This high magnetic induction is considered to be due to the formation of {hk0}〈001〉 textures. Cut cores from this material have a very low iron loss at frequencies from 400 Hz to 10 kHz.

Correlating the supercooled liquid region width with the fragility parameter in bulk metallic glasses

A linear correlation of fragility parameter D* with supercooled liquid region width ΔTx for Ca-based bulk metallic glasses (BMGs) was revealed. This relationship is found in La- and Zr-based BMGs as well and extended to several glass-forming systems. The origin of this phenomenon lies in the close relation between crystallization and temperature dependence of viscosity. This relationship can be formulated by ΔTx0.33=6.8×10-3×(D*)(Tg0.33)+2(K), indicating that the unique variation of the viscosity with the temperature correlates with the location and width of the supercooled liquid region. Moreover, an approximation of fragility parameter D* for BMGs can be evaluated by the formula.

Fabrication of Fe-6.5wt%Si Ribbons by Melt Spinning Method on Large Scale

Melt spinning method has been widely applied for fabrication of Fe-based amorphous/nanocrystalline ribbons in industry. Compared with Fe-based amorphous/nanocrystalline alloys, Fe-6.5wt%Si high silicon steel is of low cost and has comparable excellent soft magnetic properties. Due to higher melting point and absence of supercooled liquid region, fabrication of Fe-6.5wt%Si ribbons is very hard and is only on lab scale. In this paper, we report that large scale fabrication of Fe-6.5wt%Si ribbons was successful and microstructures, ordered structures, and mechanical and soft magnetic properties of the ribbons were investigated. Due to rapid solidification rate, the ribbons were of ultrafine grains, and low degree of order and exhibited some extent of bending and tensile ductility. After heat treatment, excellent soft magnetic properties were obtained. Due to near-zero magnetostriction, the ribbons are promising to be used in electric devices with high frequencies where low noises are required.

Effect of Annealing Temperature on Soft Magnetic Properties of Cold Rolled 0.30 mm Thick Fe-6.5wt.%Si Foils

0.30 mm thick and 90 mm wide thin foils made of Fe-6.5wt.%Si alloy were successfully fabricated by traditional rolling. The as-rolled sheets had good shapes and shining metal luster. The effects of annealing temperature on the magnetic properties of the sheets were investigated. Excellent Dc properties (Hc: 11.55 A/m, µm: 23710, and Bs: 1.439 T) were obtained at an annealing temperature of 1453 K for 1.5 h. At low frequencies (≤ 1 kHz), heat treatment temperature has little effect on iron loss which remained at the level of 9.8 W/kg. Annealing at 1273 K for 1.5 h is optimum for frequencies above 5 kHz.

Deformation behaviour and 6H-LPSO structure formation at nanoindentation in lamellar high Nb containing TiAl alloy

Microstructure and deformation mechanisms at a nanoindentation in the lamellar colony of high Nb containing TiAl alloy have been studied using the focused ion beam and the transmission electron microscopy. Considerable deformation twins are observed around the nanoindentation, and a strain gradient is generated. A continuous change in the bending angle of the lamellar structure can be derived, and a strain-induced grain refinement process is observed as various active deformations split the γ grains into subgrains. In addition to all possible deformation mechanisms (ordinary dislocation, super-dislocation and deformation twining) activated due to the heavy plastic deformation, a 6-layer hexagonal (6H) long-period stacking ordered structure is identified for the first time near the contact zone and is thought to be closely related to the glide of partial dislocations.

Reaction behaviors occurring in Ti/Al foil metallurgy

Reaction behaviors occurring in Ti/Al foil metallurgy were systematically investigated. Particular emphasis was focused on the reaction between solid Al and Ti as well as subsequent reaction between TiAl3 and Ti layer. In the solid reaction between Al and Ti, the presence of residual Al is mainly caused by inhomogeneous growth of TiAl3 layer and micro-voids existing at the interface. However, through reaction between molten Al and Ti, TiAl3/Ti multilayer can be achieved with complete consumption of Al. During subsequent high-temperature heat treatment, TiAl3/Ti multilayer will eventually turn into Ti3Al/TiAl multilayer accompanying with simultaneous formation and successive disappearance of intermediate phases, such as TiAl2 and Ti2Al5. Moreover, it is found that the growth direction of TiAl layer changes as a function of annealing time between different couples in multi-intermetallics system.

The effect of directionally solidified microstructures on ductility of Fe-6.5wt%Si alloy

Fe-6.5wt%Si high silicon steel has superior magenitic properties. However, such high Si content results inroom-temperature embrittlement and poor workability due to the formation of ordered intermetallic phases. Zone Melting Liquid Metal Cooling directional solidification technique was employed to produce the Fe-6.5wt%Si alloy with columnar-grained structures. The cooling rate of directional solidificationplays a critical role in maintaining the grain growth, and the rate around 3 K/s is an optimum conditionto form columnar-grained structure and to improve its ductility.

Effect of wheel speed on magnetic and mechanical properties of melt spun Fe-6.5 wt.% Si high silicon steel

Fe-Si electric steel is the most widely used soft magnetic material in electric machines and transformers. Increasing the silicon content from 3.2 wt.% to 6.5 wt.% brings about large improvement in the magnetic and electrical properties. However, 6.5 wt.% silicon steel is inherited with brittleness owing to the formation of B2 and D03 ordered phase. To obtain ductility in Fe-6.5wt.% silicon steel, the ordered phase has to be bypassed with methods like rapid cooling. In present paper, the effect of cooling rate on magnetic and mechanical properties of Fe-6.5wt.% silicon steel is studied by tuning the wheel speed during melt spinning process. The cooling rate significantly alters the ordering and microstructure, and thus the mechanical and magnetic properties. X-ray diffraction data shows that D03 ordering was fully suppressed at high wheel speeds but starts to nucleate at 10m/s and below, which correlates with the increase of Young’s modulus towards low wheel speeds as tested by nanoindentation. The grain sizes of the ribbons on the wheel side decrease with increasing wheel speeds, ranging from ∼100 μm at 1m/s to ∼8 μm at 30m/s, which lead to changes in coercivity.

Electrolytic plasma processing-an innovative treatment for surface modification of 304 stainless steel

There is widespread attention to surface profile and modification of 304 stainless steel for research development and application. Here, a successful electrolytic plasma processing (EPP) technique has been developed for both surface pretreatment and coating deposition of 304 stainless steel. Representative images confirm that the number of the pits increases and the ravines gradually disappear on the steel pretreated by EPP with the increase of processing time and applied voltage. Moreover, there is an obvious enhancement in surface roughness of 304 stainless steel after EPP pretreatment. In the case of coating deposition, the further EPP modification conducted on the pretreated sample offers a simple and effective technique for the production of zinc coatings having the features of full coverage and homogeneous distribution. The results show that a zinc coating with a thickness of approximately 0.5 μm can be obtained on the 304 stainless steel by means of EPP for only 60 s.

Nb–Al diffusion reaction in high Nb containing TiAl porous alloys

Abstract High Nb containing TiAl porous alloys were synthesised by powder metallurgy (PM). In order to reveal reaction mechanism of Nb in preparation of the porous alloys, Nb–Al diffusion reaction was investigated using diffusion couples at relatively low temperatures of 600–800°C. The porous Nb–Al diffusion layer was identified as NbAl3 phase and the thickness of diffusion layer indicated that the Nb–Al diffusion mainly occurred at 800°C. In addition, the pore diameter distribution indicated that Nb–Al diffusion also contributed to the increase in pore diameter. According to these results, the diffusion reaction model was established for high Nb containing TiAl porous alloys.