Effect of pre-annealing prior to cold rolling on the precipitation,microstructure and magnetic properties of strip-cast non-oriented electrical steels

A novel processing route involving strip casting, pre-annealing treatment, cold rolling and recrystallization annealing was applied to a Fe-2.6%Si steel to improve the magnetic properties. The impact of as-cast strip pre-annealing on the microstructure, texture, precipitation and magnetic properties were investigated by electron probe micro-analysis, transmission electron microscopy, and X-ray diffraction analysis,etc. It was found that the precipitation of second-phase particles during strip casting was restrained by rapid solidification. The absence of pre-annealing led to the occurrence of a large amount of 20–50 nm Mn S precipitates in the final annealed sheets, which is responsible for fine grains and high core loss(4.01 W/kg) due to grain boundary pinning effect. Although the microstructure and texture of 900–1000?C pre-annealed samples were similar to those of as-cast strip, significant grain coarsening together with the strengthening of-fiber texture was observed in the 1100?C pre-annealed strips. In comparison with the case of as-cast strip, a higher amount of large-sized precipitates consisting of manganese sulfide and/or aluminum nitride occurred in matrix after pre-annealing. Correspondingly, in the final annealed sheets, the number density of precipitates with sizes smaller than 100 nm was substantially reduced, and100–200 nm and 200–500 nm sized particles became more dominant in samples subjected to 30-min and 120-min pre-annealing treatments respectively. In addition, the average grain size of final annealed sheets increased with the pre-annealing temperature and time because of the weakened pining effect of coarsen precipitates. Ultimately, the magnetic induction of samples subjected to pre-annealing was slightly increased and ranged from 1.73 T to 1.75 T owing to the enhancement of {100} recrystallization texture, and simultaneously the core loss significantly decreased until a minimum of 3.26 W/kg was reached. Nevertheless, large number of 200–500 nm particles presented during pre-annealing for 120 min could weaken the improvement in core loss which is likely associated with the pinning effect on magnetic domain wall.     

Drag Effects of Solute and Second Phase Distributions on the Grain Growth Kinetics of Pre-Extruded Mg-6Zn Alloy

In order to control the grain size during hot forming,grain growth behavior of a pre-extruded Mg-6Zn magnesium alloy and its correlation with solute and second phase distribution were investigated.Isothermal annealing was conducted on a Gleeble-1500 thermo-mechanical simulator.The mean grain size Dg of each annealed specimen was measured by the quantitative metallography technique.The grain growth kinetics of the Mg-6Zn alloy annealed at 473–623 K was obtained as D D RT tg g404 11-=2.25 ×10 exp(-95450)by the least square linear regression method.The deviation of grain growth exponent n = 4 from the theoretical value of 2 may be attributed to the presence of solute zinc and second phases which will retard the boundary migration.Microscopic observations show that the non-uniform distribution of grain size for samples pre-extruded or annealed at low temperatures is closely related to the non-uniform distribution of fine and dispersed second phases but not to the non-uniform distribution of solute zinc.This indicates that second phase pinning effect plays an important role in microstructure refinement.     

Growth Behavior of α Phase in Ti-5.6Al-4.8Sn-2.0Zr-1.0Mo-0.35Si-0.7Nd Titanium Alloy

The thermal stability of the microstructure of a near-α titanium alloy after aging at 750℃ was investigated using optical microscope and transmission electron microscope as well as composition analysis. Aging treatment brings about significant coarsening of grain boundary α and α platelets within the colonies for martensitic microstructure. The observed changes are related to the growth steps or ledges of the interface and lamellar termination presented in the microstructure. The composition analysis of the coarsened α plate is consistent with the growth kinetics. The α Widmanstatten plates were coarsened due to the movement of α/β interface for Widmanstatten microstructure, and the phase boundaries of primary α (αp) phase directly moved into the transformed β for bimodal microstructure.     

Growth Behavior of α Phase in Ti-5.6Al-4.8Sn-2.0Zr-1.0Mo-0.35Si-0.7Nd Titanium Alloy

The thermal stability of the microstructure of a near-α titanium alloy after aging at 750℃ was investigated using optical microscope and transmission electron microscope as well as composition analysis. Aging treatment brings about significant coarsening of grain boundary α and α platelets within the colonies for martensitic microstructure. The observed changes are related to the growth steps or ledges of the interface and lamellar termination presented in the microstructure. The composition analysis of the coarsened α plate is consistent with the growth kinetics. The α Widmanstaetten plates were coarsened due to the movement of α /β interface for Widmanstaetten microstructure, and the phase boundaries of primary α（αp） phase directly moved into the transformed β for bimodal microstructure.     

Formation Behavior of 14H Long Period Stacking Ordered Structure in Mg–Y–Zn Cast Alloys with Different α-Mg Fractions

Phase compositions and microstructure evolutions of three Mg–Y–Zn cast alloys during isothermal annealing at 773 K have been systematically investigated to clarify the formation behavior of 14 H long period stacking ordered(LPSO) structure from α-Mg grains.The annealed microstructure characteristics indicate that the 18 R phase is thermal stable in Mg86Y8Zn6 alloy where 18 R serves as matrix,and 14 H lamellar phase only forms within tiny α-Mg slices(less than 1% for volume fraction).The α-Mg grains in Mg88Y8Zn4 and Mg89Y8Zn3 alloys exhibit cellular shape,and 14 H phase forms and develops into lamellar shape in these cellular grains after annealing.The results suggest that the presence of α-Mg grains is a requirement for the generation of 14 H phase.The nucleation and growth rates of 14 H lamellas are accelerated in α-Mg grains with higher concentrations of stacking faults and solute atoms.Moreover,the 14 H lamellas are parallel to adjacent 18 R plates in Mg86Y8Zn6 alloy,but the 14 H phase precipitated in cellularα-Mg grains of Mg88Y8Zn4 and Mg89Y8Zn3 alloys exhibits random orientation relationship with surrounding 18 R phase,indicating that the orientation relationship between 14 H and 18 R phases depends on the relationship between α-Mg grains and 18 R phase.     

Effect of Ni Contents on the Microstructure and Mechanical Properties of Martensitic Stainless Steel Guide Roll by Centrifugal Casting

A novel process based on centrifugal casting was developed to produce martensitic stainless steel for guideroll materials. Centrifugal casting provides a lower production cost and less of the thermal cracking defects which normally occur in the overlaid welding process. In this study, the effects of Ni on the microstructure and mechanical properties of martensitic stainless steel were investigated. The results show that the addition of Ni resulted in a decrease in the volume fraction of delta ferrite and an increase in the volume fraction of the retained austenite, respectively. Moreover, a tensile strength of 1600 MPa with an elongation of 4% were obtained after tempering at 500℃ for 2 h. These values were higher than those obtained by using the conventional overlaid process.     

Growth Behavior of a Phase in Ti-5.6Al-4.8Sn-2.0Zr-1.OMo-0.35Si-0.7Nd Titanium Alloy

The thermal stability of the microstructure of a near-αtitanium alloy after aging at 750℃was investigated using optical microscope and transmission electron microscope as well as composition analysis. Aging treatment brings about significant coarsening of grain boundaryαandαplatelets within the colonies for martensitic microstructure. The observed changes are related to the growth steps or ledges of the interface and lamellar termination presented in the microstructure. The composition analysis of the coarsenedαplate is consistent with the growth kinetics. TheαWidmanstatten plates were coarsened due to the movement ofα/βinterface for Widmansta'tten microstructure, and the phase boundaries of primaryα(αp) phase directly moved into the transformedβfor bimodal microstructure.     

Friction stir spot welding of SPCC low carbon steel plates at extremely low welding temperature

Friction stir spot welding(FSSW) was applied to 2.0 mm thick steel plate cold-rolled commercial(SPCC)low carbon steel plates at a very low rotation speed that ranged from 5 to 50 rpm, which was much lower than that generally used for the conventional FSSW technique. Due to the very low heat input, the welding processes could therefore be completed at a peak welding temperature below 160℃. As a result,a significantly refined microstructure with an average grain size of about 0.41 μm was formed in the stir zone of the joints and the J1{0–11}-211 and J2{1–10}-1–12 shear textures were the dominant components, which are different from the D1{11–2}111 and D2{-1–12}111 shear textures formed in the conventional FSSW joints. In addition, no heat affected zone could be detected along the crosssectional plane of the joints. Although a few void-like non-bonded areas were still observed along the interface between the upper and lower steel plates, the shear tensile loads of the joints increased to about 10.0 kN when welded at a condition of 8 t, 20 rpm and 30s, and the joints fractured through the plug failure mode.     

Microstructural Evolution of Solid-solution-treated Zn-22Al in the Semisolid State

The effect of solid-solution-treatment on the semisolid microstructure of Zn—22AI with developed dendrites was investigated.Forming Zn—22AI products by semisolid metal processing offers significant advantages,such as reductions in macro-segregation,porosity and forming costs.Thermal and microstructural analyses of the formed Zn—22AI alloy were performed by differential scanning calorimetry,scanning electron microscopy and optical microscopy.The changes in the microstructures and phase transformation in response to various solid-solution -treatments were analysed.In this study,as-cast samples were held isothermally at 330℃for 0.5—5 h and then partially remelted at a semisolid temperature of 438℃for 1 h to produce a solid-globular grain structure in a liquid matrix.A non-dendritic semisolid microstructure could not be obtained when the traditionally cast Zn—22AI alloy with developed dendrites was subjected directly to partial remelting.After solid-solution-treatment at 330℃,the black interdendritic eutectics were dissolved,and the dendritic structures gradually transformed into uniformβstructures when the treatment time was increased.The coarsened and merged dendrites were separated as a result of penetration by the liquid phase and melting of the residual eutectic at sites along the former grain boundaries.The microstructure of the solid-solution-treated sample transformed into a small globular structure;the best shape factor of 0.9,corresponding to a particle size of 40±16μm,is achieved when the sample was treated for 3 h followed by direct partial remelting into its semisolid zone.     

Microhardness,Microstructure and Electrochemical Efficiency of an Al(Zn/xMg) Alloy after Thermal Treatment

The influence of Mg on the microhardness,microstructure and electrochemical efficiency of Al(Zn/xMg) alloys have been investigated.Al(Zn/xMg) alloys were prepared by metal mould casting method to diminish the process cost and to generate an alloy with homogenous microstructure and less casting porosity.Vickers hardness,X-ray diffraction,scanning electron microscopy and transmission electron microscopy were performed to determine the Mg influence on the AlZn alloy.Electrochemical efficiency was used to relate the influence of Mg with the thermal treatment on the corrosion behavior of the Al(Zn/xMg) alloy.The results reveals the presence of Al 32(MgZn) 49 phase for two events;the first is when the Mg content is above 5.49% in as-cast condition,and the second after the thermal treatment is carried out at 450℃ for 5 h.The results also show that the microhardness and electrochemical efficiency have been influenced by the presence of Al 32(MgZn) 49 phase.The addition of Mg modifies the microstructure,increases the content of Al 32(MgZn) 49 phase and improves the electrochemical efficiency.     

Oxygen Behavior in Bulk Amorphous Zr—base Alloy

Bulk Zr55Al10Ni5Cu30 metallic glass plates with a dimension of 85 mm×35mm×4 mm and a complicated plate were fabricated by injecting casting method using spongy zirconium and industrial purity aluminum, nickel and copper as raw materials. It was shown that the holding time of liquid metals at elevated temperatures had a great influence on the oxygen content of the plates due to the contamination resulting from the atmosphere. Increasing holding time resulted in the increase of oxygen content in the injected alloy. The glass transition temperatures of the bulk metallic glass plates are higher than that reported in the literature and crystallization temperature is lower for the one with higher oxygen content at the same heating rate. The extension of the undercooled liquid region △Tx reaching about 87 K is 3 K higher than that previously reported and 26 K higher than that with oxygen content of 0.076 wt pct for the one with oxygen content as high as 0.065 wt pct. Therefore the oxygen content of the alloy has     

Crystallization Kinetics of Nanophase Glass-Ceramics as Magnetic Disk Substrate

Glass-ceramics containing β-quartz as a main crystal phase based on the system of SiO2-Al2O3-Li2O-K2O-MgO-ZnO were investigated for the application to magnetic storage substrate for higher storage capacity. Parent glasses were prepared, then nucleated and crystallized at certain temperatures for 3-4 h. The crystallization kinetics of glass-ceramics was also studied. The grain size was estimated by Scherrer formula and image treatment of transmission electron microscopy （TEM）. The results showed that the Avrami exponent was determined to be 3.88, the activation energy 189.3＋7 k J/tool and the grain size 30-60 nm. A detailed microstructure of the glass-ceramics, including grain distribution and the morphology of nano-crystalline was characterized by TEM, X-ray diffraction （XRD）, differential scanning calorimeter （DSC）, differential thermal analysis （DTA）. The relationship between microstructure and mechanical properties was also discussed.     

Selective Laser Melting of an Al–Fe–V–Si Alloy: Microstructural Evolution and Thermal Stability

Selective laser melting was used to produce an aluminum alloy Al-8.5Fe-1.3V-1.7Si(wt%). The effects of heat treatment on microstructure evolution and phase stability during long-term thermal exposure of the deposits were investigated. Results show that the microquasi-crystalline phase, Al12(Fe,V)3Si and AlmF e metastable phases coexisted with α-Al in the as-produced alloy. Annealing at 400 °C resulted in decomposition of microquasi-crystalline phase and supersaturated α-Al into Al12(Fe, V)3Si phase in the fusion zone, accompanied by the decrease in alloy hardness. The activation energy of this decomposition process was 115 k J/mol. A more homogenous microstructure was obtained after annealing at 400 °C for 60 min,which was resistant to coarsening exposed at 425 °C up to 500 h. The Al12(Fe,V)3Si and AlmF e phases were coarsened at 475 and 525 °C with increasing the exposure time. Coarsening of Al12(Fe,V)3Si phase was attributed to a combination of volume diffusion and grain boundary diffusion mechanism of Fe. Heat treatment at 600 °C resulted in accelerated microstructure coarsening and formation of large-sized equilibrium phases, which signi?cantly degraded the room temperature microhardness.     

Effects of Oxygen on the Microstructure of Ti_(47)Al_(0.7)B Alloys

The effects of oxygen on the microstructure of Ti-47Al-0.7B (at. pct) alloy for as-cast automotive valves were investigated. Six alloys with oxygen content from 0.4 to 1.4 at. pct were prepared by induction melting and centrifugal casting in CaO crucible under protective atmosphere. The microstructures were observed by optical microscopy (OM) and scanning electron microscope (SEM). The results show that the increase of oxygen content led to grain refinement and enhanced the microhardness as well as the α 2 ...     

Si-Al-Ir Oxidation Resistant Coating for Carbon/Carbon Composites by Slurry Dipping

A Si-Al-Ir oxidation resistant coating was prepared for SiC coated carbon/carbon composites by slurry dipping. The phase composition, microstructure and oxidation resistance of the as-prepared Si-Al-Ir coating were studied by XRD (X-ray diffraction), SEM (scanning electron microscopy), and isothermal oxidation test at 1773 K in air, respectively. The surface of the as-prepared Si-Al-Ir coating was dense and the thickness was approximately 100 μm. Its anti-oxidation property was superior to that of the inner...     

Magnetism and Magnetocaloric Properties of Mn3Zn1-xSnxC and Mn3-xCrxZnC Compounds

Upon substitution of Sn for Zn,the Curie temperature of Mn 3 ZnC is lowered from 380 to 375 K for Mn 3 Zn 0.95 Sn 0.05 C and to 305 K for Mn 3 Zn 0.75 Sn 0.25 C.In accordance with the second-order ferromagneticparamagnetic transition,a room-temperature magnetocaloric effect without thermal and magnetic hysteresis is observed over a wide temperature range.The maximum value of the magnetic-entropy change S M for a magnetic-field change from 0 to 5 T is 2.42 J.kg 1.K 1 at 386 K for Mn 3 Zn 0.95 Sn 0.05 C and 1.70 J.kg 1.K 1 at 308 K for Mn 3 Zn 0.75 Sn 0.25 C.Meanwhile,substitution of Cr for Mn lowers the temperature of ferromagneticferrimagnetic transition from 233 K for Mn 3 ZnC to 230 K for Mn 2.9 Cr 0.1 ZnC and to 175 K for Mn 2.1 Cr 0.9 ZnC.An inverse magnetocaloric effect with S M equal to 0.28 J.kg 1.K 1 at 223 K for a field change from 0 to 1.47 T is observed for Mn 2.9 Cr 0.1 ZnC.     

Enhanced Strength and Ductility Due to Microstructure Refinement and Texture Weakening of the GW102K Alloy by Cyclic Extrusion Compression

The cyclic extrusion compression(CEC) was applied to severely deform the as-extruded GW102K(Mg–10.0Gd–2.0Y–0.5Zr, wt%) alloy at 350, 400, and 450 °C, respectively. The microstructure, texture, and grain boundary character distribution of the CECed alloy were investigated in the present work. The mechanical properties were measured by uniaxial tension at room temperature. The crack initiation on the longitudinal section near the tensile fracture-surface was investigated by high-resolution scanning electron microscopy(SEM). The result shows that the microstructure was dramatically refined by dynamic recrystallization(DRX). The initial fiber texture was disintegrated and obviously weakened. The 8-passes/350 °C CECed alloy exhibited yield strength of 318 MPa with an elongation-to-fracture of 16.8%, increased by 41.3% and 162.5%, respectively. Moreover, the elongation-to-fracture of the 8-passes/450 °C CECed alloy significantly increased more than 3 times than that of the received alloy. The cracks were mainly initiated at twin boundaries and second phase/matrix interfaces during tensile deformation. The microstructure refinement was considered to result in the dramatically enhanced of the strength and ductility. In addition, the texture randomization during CEC is beneficial for enhancing ductility. The standard positive Hall–Petch relationships have been obtained for the CECed GW102 K alloy.     

SiC-Si-ZrSiO_4 Multiphase Oxidation Protective Coating for Carbon/Carbon Composites

In order to improve the anti-oxidation property of carbon/carbon （C/C） composites, a novel SiC-Si-ZrSiO4 multiphase oxidation protective coating was produced on the surface of C/SiC coated carbon/carbon compo ites by a pack cementation technique. The phase composition and microstructure of the as-prepared coatings were characterized by XRD （X-ray diffraction）, SEM （scanning electron microscopy） and EDS （energy dispersive spectroscopy）. Oxidation behavior of the multiphase coated C/C composites was also investigated. It showed that the as-prepared coating characterized by excellent oxidation resistance and thermal shock re- sistance could effectively protect C/C composites from oxidation at 1773 K for 57 h in air and endure the thermal cycle between 1773 K and room temperature for 12 times, whereas the corresponding weight loss is only 1.47%. The excellent oxidation protective ability of the SiC-Si-ZrSiO4 coating could be attributed to the C/SiC gradient inner layer and the multiphase microstructure of the coating.     

Effect of Heat Treatment on the Microstructure and Residual Stresses in (Ti,Al)N Films

(Ti,Al)N films were fabricated by arc ion plating (AIP) and then annealed within a range of temperatures from 200 to 500~0C for 30 min in vacuum. The results indicate that the average residual stresses decrease slightly from -5.84 to -4.98 GPa with increasing annealing temperature. The stress depth distribution evolves from a sharp "bell" shape to a mild "bell" shape, suggesting a more uniform stress state in the annealed films. The microstructure of the films was also investigated in detail. The as-deposited film consists of fine columnar crystals with an amorphous phase at the interface. During heat treatment, the columnar subgrain growth was observed; meanwhile, the phenomenon of crystallization has been identified at the interface. Further more, the relationship between the residual stresses and the microstructure of the films was explored and highlighted. In addition, there is no hardness degradation of the films during heat treatment.