Effect of rare earth cerium and impurity tin on the hot ductility of a Cr-Mo low alloy steel

The specimens of 1Cr-0.5Mo low alloy steel, undoped, Sn-doped and Ce+Sn-doped, were austenitized at 1300 oC and then cooled down to different temperatures in the range of 700–1050 oC, followed by tensile tests with the aid of a Gleeble machine. The reduction of area(RA) obtained from the test was employed to evaluate the hot ductility of the steel. The tested specimens were characterized using different techniques. Minor Sn could considerably reduce the RA values of the steel in the whole temperature range, and the hot ductility curve could be widened and deepened. Nevertheless, minor Ce could improve the hot ductility of the Ce+Sn-doped steel by fully suppressing the Sn-induced hot ductility deterioration. FEGSTEM microanalysis showed that the Sn or Ce and Sn atoms segregated to austenite grain boundaries in the Sn-doped or Ce+Sn doped specimens. The detrimental effect of Sn on the hot ductility could be attributed mainly to the segregation of Sn as it could decrease the grain boundary cohesion and in turn enhanced the grain boundary sliding and cracking. However, this detrimental effect of Sn could be counteracted by the segregation of Ce which could increase the grain boundary cohesion and in turn restrained the grain boundary sliding and cracking. Accordingly, a minor addition of rare earth Ce could be an effective method of suppressing the detrimental effect of impurity elements on the hot ductility of a Cr-Mo low alloy steel.     

Influence of Zr Additions on Microstructure and Magnetic Properties of Nanocomposite Nd10.5Fe78-xCo5ZrxB6.5（x=0-5） Alloys

The influence of Zr addition on the microstructure and magnetic properties of nanocomposite Nd10.5Fe78-x Co5ZrxB6.5(x=0-5)alloys was investigated. It was found that the intrinsic coercivity could be significantly improved by the addition of 2% (atom fraction) Zr. The presence of small amount of amorphous phase is responsible for tile low intrinsic coercivity for Zr-free alloy. The small amount addition of Zr may suppress the growth of grains of α-Fe and Nd2Fe14B phases. The more homogeneous microstrueture with an average grain size of 20 nm can be obtained for Nd10.5 Fe76 Co5Zr2B6.5 alloy.     

Influence of Solution Treatment on Microstructure of AEREX350 Alloy

The microstructure of hot rolled AEREX350 alloy under various solution treatments was investigated by scanning electron microscope (SEM) and transmission electron microscope (TEM). It was found that with increasing solution temperature,η phase precipitated firstly at grain boundaries in parallel at 800℃ and then within grains at about 980℃. The η phase precipitated at grain boundaries played a role in preventing the migration of grain boundaries,and the η phase precipitated within grains would form Widmannsttten structure with further increasing solution temperature. η phase precipitated at grain boundaries was dissolved at temperature ranging from 1080℃ to 1095℃,resulting in grain growth promptly owing to release of the pinning effect on grain boundaries. γ' phase precipitated during the process of air cooling after hot rolling and dissolved at temperature ranging between 1010℃ and 1020℃.     

Mechanism of Embrittlement and De-Embrittlement for 2.25Cr-1Mo Steel

 The constant embrittlement curve for constant segregation concentration on grain boundary of impurity element P and relationship between equilibrium grain boundary segregation concentration and operation time for 225Cr-1Mo steel were derived based on the theory of equilibrium grain boundary segregation. The mechanism of step-cooling test and mechanism of de-embrittlement for 225Cr-1Mo steel were explained. The segregation rate will increase but equilibrium grain boundary segregation concentration of impurity element P will decrease as temperature increases in the range of temper embrittlement temperature. There is one critical temperature of embrittlement corresponding to each embrittlement degree. When the further heat treating temperature is higher than critical temperature, the heat treating will become a de-embrittlement process; otherwise, it will be an embrittlement process. The critical temperature of embrittlement will shift to the direction of low temperature as further embrittlement. As a result, some stages of step-cooling test would change into a de-embrittlement process. The grain boundary desegregation function of impurity element P was deduced based on the theory of element diffusion, and the theoretical calculation and experimental results show that the further embrittlement or de-embrittlement mechanism can be interpreted qualitatively and quantitatively by combining the theory of equilibrium grain boundary segregation with constant embrittlement curve.     

Evolution of Sm2Fel7 Alloys during Hydrogenation-Disproportion Process

The evolution of phase compositions, phase change and microstructure in Sm2Fe17 alloys during hydrogenationdisproportion process were systematically studied with XRD, SEM, EDX methods. Research indicates that HD process of Sm2Fe17 alloys is as follows： Sm2Fe17 alloy absorbs hydrogen first in the atmosphere of hydrogenation with a pressure of 0.1 MPa. Disproportionation begins at T ≥ 500 ℃, then the alloys tuna into lots of SmHx and α-Fe phases which are partly in microcrystal or amorphous structures. Along with the increase of temperature, the microcrystal and amorphous structures transformed into crystal structure and this transformation thoroughly completed at 750 ℃. The size of obtained crystal grain is about 20 - 100 nm. Based on the experimental data, a microstructural transformation model of Sm2Fe17 alloys during hydrogenation-disproportion process was made.     

Effect of Neodymium on Microstructure and Mechanical Properties of Mg-Sb Alloy

The effects of Nd on the microstructure and mechanical properties of Mg-Sb3 alloy were studied with the 0～0.15% addition content. The addition of Nd makes the grain of Mg-Sb3 alloy obviously refined, where the grain size decreases from 100～200 μm to 0.2～10 μm. And the typical dendrite characteristic turns into the equiaxed grain microstructure with the addition of 0.05%～0.1% Nd. The reason for grain refinement is from the supercooling theory. The mechanical properties tested indicate that the tensile strength and especially elongation of the alloys are improved with the addition of Nd and their maximum enhancing rates based on the Nd-free Mg-Sb3 alloy are 20% and 10% at 0.1% Nd, respectively. The main reason is attributed to the grain refinement by Nd. The tensile strength and especially elongation decline when Nd addition is over 0.1%, owing to the number and size increase of the needle-shaped phases on the grain boundaries with the Nd addition increasing.     

织构对Cu-Al-Mn系形状记忆合金内耗的影响

In-situ observations on α/γ phase transformation were made to study the effects of grain boundary microstructures on the formation of a new phase and the migration of α/γ interphase boundary in an iron4. 2%Cr alloy. It was found that triple junctions with more random boundaries could be the primary nucleation sites for a new phase, while triple junctions with low angle or low ∑ coincidence boundaries did not play any role as preferential sites. The migration of α/γ interphase boundary during heating over the transformation temperature range showed the two stage behaviour characterized by a stage with a migration velocity of 0. 33-0. 75 mm/s and secondly by a stage with 3. 7-7. 6 mm/s. It was also found that abnormal grain growth and a high density of ∑3 coincidence boundaries could occur in a phase with bcc structure after cycling of α/γ phase transformation. A new mechanism of nucleation and growth of a new phase in α/γ phase transformation is proposed on the basis of roles of plane-matching interphase boundaries, as previously discussed on the origin of anisotropy of grain growth due to the migration of {110} plane-matching boundaries in Fe-3z%Si alloy. The most recent theoretical work on the distribution of plane-matching boundaries in solids with different crystal structures was found to be useful for the understanding of nucleation and growth during α/γ phase transformation.     

Microstructure evolution and corrosion properties of Mg-Dy-Zn alloy during cooling after solution treatment

Microstructure evolution and corrosion properties of Mg-2Dy-0.5Zn(at.%) alloy during cooling after solution treatment were investigated.The microstructure of alloy in the solid solution state(530 oC,12 h) was composed of α-Mg and small amounts of(Mg,Zn)_x Dy phases.During cooling at a cooling rate of 2 oC/min,the 14H-type LPSO phase gradually precipitated in the grain interior and its volume fraction increased with increasing cooling time.The alloy cooled for 20 min exhibited the highest hardness value.In addition,electrochemical and immersion test results indicated that the alloy cooled for 5 min exhibited small corrosion current and low corrosion rate.The good corrosion resistance of alloy was mainly attributed to the continuous distribution of LPSO phase along the grain boundary.     

Fe-4.2%Cr合金α/γ相变中相边界移动和晶粒长大的原位观察

In-situ observations on α/γ phase transformation were made to study the effects of grain boundary microstructures on the formation of a new phase and the migration of α/γ interphase boundary in an iron-4. 2%Cr alloy. It was found that triple junctions with more random boundaries could be the primary nucleation sites for a new phase, while triple junctions with low angle or low ∑ coincidence boundaries did not play any role as preferential sites. The migration of α/γ interphase boundary during heating over the transformation temperature range showed the two stage behaviour characterized by a stage with a migration velocity of 0. 33～0. 75 mm/s and secondly by a stage with 3. 7～7. 6 mm/s. It was also found that abnormal grain growth and a high density of ∑3 coincidence boundaries could occur in a phase with bcc structure after cycling of α/γ phase transformation. A new mechanism of nucleation and growth of a new phase in α/γ phase transformation is proposed on the basis of roles of plane-matching interphase boundaries, as previously discussed on the origin of anisotropy of grain growth due to the migration of {110} plane-matching boundaries in Fe-3%Si alloy. The most recent theoretical work on the distribution of plane-matching boundaries in solids with different crystal structures was found to be useful for the understanding of nucleation and growth during α/γ phase transformation.     

Evolution of Solidification Structure of Hypereutectic Al-Si Alloy Under a Novel Low-Voltage Alternating Current Pulse

The effect of a novel low-voltage alternating current pulse（ACP）controlled by transformer and silicon controlled rectifier on the solidification structure of Al-20%Si alloy was investigated.The results indicated that the remarkable segregation of primary Si occurred during the solidification,and even dendrites ofα-Al phase appeared at the center of samples under ACP.The thickness of segregation layer decreased first and then increased with current density increasing from 0 to 300 Acm^-2.The primary Si existed with long pole or five petal star-shaped without ACP.However,the morphology of primary Si phases changed to block under ACP,and the sizes of blocky Si decreased obviously with increasing current density from 110 to 300 Acm^-2.The formation mechanism of the structure of hypereutectic Al-20%Si alloy was also discussed under ACP.     

Surface modification of （Tb,Dy）Fe_2 alloy by nitrogen ion implantation

Effects of nitriding modification on surface phase structure, morphology, corrosion resistance and magnetostriction of (Tb,Dy)Fe2 alloy were investigated by nitrogen ion implantation. Results showed that the surface REFe2 phase gradually decomposed and transformed into REN, α-Fe and Fe8N phases with the increase of nitrogen ion implantation dose. The surface morphology of the alloy had an obvious change after nitrogen ion implantation. The corrosion resistance properties of the alloy in acidic, alkaline and chloridion environment were also greatly improved. In addition, the magnetostriction performance of the alloy was almost not affected by ion implantation as the nitrided layer was quite thin and the operating temperature was very low. The results proved that nitrogen ion implantation was an effective method for surface modification of (Tb,Dy)Fe2 alloy.     

Effects of Yttrium and Cerium on Compression Properties of Ni_3Al-Base Alloys

The effects of yttrium and cerium on the compression properties of Ni_3Al-base alloys have beeninvestigated.The results reveal that the addition of about 0.1 wt% Y to Ni_3Al-B alloy is effective for improvingthe ductility at 1100℃.A ductility increase of about 100% is observed for this Y doped alloy.The yttrium re-fines grains of the alloy.An YNi_5 phase is found to be precipitated on the grain boundaries in the alloy con-taining 0.3 wt% Yor more.Adding about 0.1 wt% Ce to Ni_3Al-B-Cr-Zr alloy obviously improves the ductilityof the alloy at 1100℃.A ductility increase of about 50% is obtained for this alloy.The added cerium also pre-vents the formation of γ+γ' eutectic and refines it.The bulk phase of CeNi_4 appeares at the front of the eutecticin the alloys containing 0.1 wt% Ce or more.     

Investigation on the hot ductility of Fe-36Ni invar alloy with cerium addition

The hot ductility of Fe-36 Ni invar alloy with different additions of the element cerium was investigated using a Gleeble-3800 thermal-mechanical simulator over the temperature range 850- 1 050 ℃,and the improvement mechanism of the hot ductility was analyzed using a combination of SEM,EDS,and OM. The results indicated that Fe-36 Ni invar alloy exhibited poor hot ductility below 1 050 ℃,which was mainly attributed to weak grain boundaries and the action of grain boundary sliding. However,the alloys with cerium contents of 0. 016% and 0. 024% both demonstrated substantial improvement in the hot ductility over the entire testing temperature range. The observed improvement of the hot ductility of the alloy with 0. 016% cerium at 950 ℃ and the alloy with 0. 024% cerium at 900℃ was associated mainly with the grain boundary strengthening and the restriction of the grain boundary sliding because the addition of cerium reduced the segregation of sulfur at grain boundaries and refined the grain structure.The occurrence and acceleration of dynamic recrystallization were found to be responsible for the high hot ductility of the alloy with 0. 016% cerium at 1 000 ℃ and the alloy with 0. 024% cerium at 950- 1 000 ℃ as a result of the refinement of the grain structure by addition of cerium.     

Effect of Hot Pressing on Microstructure and Mechanical Properties of Bulk Nanocrystalline Fe3Al Materials Containing Manganese Element

 Bulk nanocrystalline Fe3Al materials containing manganese of 10% were prepared by aluminothermic reaction. Hot pressing of those materials was performed at different temperatures and times. The microstructures of the alloy were investigated by optical microscope (OM) and electron probe microanalyzer (EPMA). The grain sizes of the materials were analyzed by X-ray diffraction (XRD) and transmission electron microscope (TEM). The results showed that the grain sizes of the materials increase after hot pressing. The grain sizes of the materials decrease with increasing the hot pressing times at the same temperature and the grain sizes of the materials increase with increasing hot pressing temperatures at identical times. The hardness and compressibility of the materials were also tested. The results showed that the hardness decreases with increasing hot pressing times at 800 ℃ and hardness increases with increasing the hot pressing temperatures. The variation of hardness with grain size of the nanocrystalline Fe3Al materials after hot pressing is contrary to the Hall-Petch relation. The materials are not broken during hot pressing and exhibit good plasticity and compressibility.     

Effects of process parameters on surface quality,composition segregation,microstructure and properties of QSn6.5-0.1 alloy slabs fabricated by HCCM horizontal continuous casting

Columnar-grained QSn6. 5-0. 1 alloy slabs with a width of 70 mm and thickness of 10 mm were fabricated by heating-cooling combined mold( HCCM) horizontal continuous casting. The effects of process parameters on solidification microstructure,surface quality,composition segregation and mechanical properties were studied. The results showed that the slabs with good surface quality,excellent mechanical properties and no obvious segregation could be prepared at the melt casting temperature of 1 250 ℃,the heating-mold temperature of 1 150- 1 200℃,the cooling water flow rate of 600 L / h and the casting speed of 20- 80 mm / min. The slabs had the yield strength of 124- 155 MPa,the elongation rate of 46. 6%- 56. 3% and the surface roughness of 0. 22- 0. 55μm,which enabled them to be directly processed without subsequent milling surface. The ratio of Sn content in the surface to that in the core was 0. 83- 1. 10,with an average value close to 1. 0,and not obviously influenced by process parameters. When the casting speed increased from 20 to 80 mm / min,the grain size changed little if the other process parameters were the same. When the heating-mold temperature increased from 1 150 to 1 200℃,the grain size was obviously refined and became more uniform if the casting speed was the same. Within the range of the casting speed at which the columnar grain structure could be obtained,the columnar grain size was mainly influenced by the heating-mold temperature.     

Grain refinement of AZ31 magnesium alloy by AI-Ti-C-Y master ahoy

Al-Ti-C-Y master alloy was prepared by combining SHS technique and melting-casting method. The microstructure of master alloy and its grain-refining effect on AZ31 alloy were investigated by means of OM, XRD, SEM and EDS. Experimental results indicated that the prepared master alloy consisted of α-Al, TiAl3, TiC and Al3Y phases, and exhibited good grain-refining performance of AZ31 alloy. Morphology of α-Mg changed from coarse dendritic to free equiaxed and the average grain size of α-Mg matrix reduced from the original 580 to 170 μm after adding 1.0 wt.% master alloy. The grain refining efficiency of Al-Ti-C-Y master alloy on AZ31 alloy was mainly attributed to heterogeneous nucleation of TiC particles and grain growth restriction of Al-Y compound or TiC at grain boundaries.     

Effect of Lanthanum on Driving Force for Cu6Sn5 Growth and Improvement of Solder Joint Reliability

By means of adding low content of rare earth element La into Sn6(bPb40 solder alloy, the growth of Cu6Sn5 intermetallic compound at the interface of solder joint is hindered, and the thermal fatigue life of solder joint is increased by 2 times. The results of thermodynamic calculation based on diffusion kinetics show that, the driving force for Cu6Sn5 growth is lowered by adding small content of La in Sn60-Pb40 solder alloy. Meanwhile, there is aneffective local mole fraction range of La, in which, 0.18% is the limited value and 0.08% is the best value.     

Influence of strontium and lanthanum simultaneous addition on microstructure and mechanical properties of the secondary Al-Si-Cu-Fe alloy

In this paper, modification agents with different contents of Sr and La elements were added into Al-Si-Cu-Fe alloy and the effect on refinement of secondary phases and α-Al grain was investigated by optical microscopy, scanning electronic microscopy and X-ray diffractometry. Tensile testing was carried out to characterize the strength of the alloys. The XRD result indicated that Fe_9LaSi_4 and SrSi_2 phases were formed after Sr and La elements were added in the alloys simultaneously. With the help of metallographic analysis techniques, the length of needle-like phases, mainly composed of eutectic Si and β-Fe, was quantified. And the secondary dendrite arm spacing(SDAS) of α-Al grain was also evaluated. The quantification results indicated that the modification agents with different contents of Sr and La elements showed varied refinement effects on the mean length of needle-like phases and SDAS value. When the addition amount increased, the length of needle-like phase and SDAS value were decreased. The minimum mean length of needle-like phases(Sr/La=1:1) and the SDAS value(Sr/La=1:5) were obtained by setting the addition amount of the modification agent at 0.12 wt.%. The yield strength of the alloy was related to the mean SDAS value, whilst the ultimate tensile strength, elongation and hardness values were related to the mean length of needle-like phase.     

Metallurgical Source of Cryogenic Intergr anular Fracture of Fe-38Mn Austenitic Alloy

SEM and Field emitting TEM-EDAX were used to investigate the fracture surface of series impact specimens and the grain boundary chemistries of VIM (vacuum-induction-melted) Fe-38Mn austenitic alloy before and after ESR (electroslag remelting,). The quantity and the size of inclusions were also examined. The results show that the VIM Fe-38Mn aust enitinic alloy water-quenched from 1 100 ℃ undergoes an obvious ductile-to-brittle transition, and the impact work at ambient temperature is 242 J, the corresponding fracture surface exhibits adimple character. However, the impact work at 77 K of VIM alloy is only 25 J and the fracture mode is IGF (intergranular f racture). After ESR, the impact work at ambient temperature is 320 J and the fra cture surface exhibits a character of "volcano lava" (meaning excellent toughn ess); The impact work at 77 K is up to 300 J and the fracture mode is microvoid coalescence mixed with quasi-cleavage. The segregation of Mn is not found in all specimens, but the segregation of S is observed, and the S segregation is decreased after ESR. The examined results of inclusions show that ESR reduces the quantity and improves the morphology of inclusions. From the above results it can be seen that the cryogenic IGF of VIM Fe-38Mn austenitic alloy is related to the S segregation at grain boundary. After ESR the decrease in the quantity and size of inclusion results in the increase of the impact work at ambient temperature, while the restriction of IGF is related to the decrease in the total level, and hence in the grain boundary segregation of S.     

Differences of element distribution between free and wheel side surface of NdFeB/α-Fe ribbons

The ribbons of NdFeB/α-Fe composite alloy were prepared by melt spinning and post crystallizing technique.The element distri-butions and phase component of both surfaces of as-spun ribbons were measured by energy dispersive spectrometry (EDS) and X-ray diffrac-tion (XRD).Because of the centrifugation,a segregation of B,Fe,and Nd concentrations was observed at the cross section.After crystallizing annealing,the element concentration segregation still existed in the as-crystallized ribbons.Due to the segregation of B,Fe,and Nd,the B-rich phase was observed near the wheel side surface.The B-rich phase may deteriorate the magnetic property of NdFeB/α-Fe composite alloy.