Effect of matrix microstructure on precipitation of Laves phase in Fe–10Cr–1.4W(–Co) alloys

Ferritic heat-resistant steels involving intermetallic Laves phase have drawn a growing interest for the enhancement of creep strength, while the brittleness of Laves phase may lower the toughness of the alloy. We believe it is possible to modify the morphology of Laves phase precipitates by controlling the α-Fe matrix microstructure. In order to make clear the influence of matrix microstructures on age-hardening, the precipitation behavior of Laves phase was investigated by transmission electron microscopy (TEM). The matrix of the Fe–10Cr–1.4W–4.5Co (at%) alloy is controlled by heat treatments so as to provide three types of microstructures; ferrite, ferrite+martensite, and martensite. Alloys with ferrite and ferrite+martensite matrices show age-hardening behavior comprised of two hardness peaks. At around the first hardness peak, it is revealed by TEM observation that fine particles precipitate coherently within the ferrite matrix. In the martensite matrix, most of R-phase and Laves phase precipitates exist on laths and dislocations.     

A study of impact toughness of Fe-Cr-X damping alloys

A study was carried out on the impact toughness of Fe- Cr- Х damping alloys. Two measures proved to be effective in improving impact toughness. One was to lower carbon plus nitrogen content to an ultra- low level. This method is suitable for single- phase ferrite alloy. The other is to use dual- phase damping alloys. The presence of martensite in Fe- Cr- Х alloys can enhance impact toughness remarkably, but lower damping capacity drastically. This shows the importance of achieving balance between mechanical prop-erties and damping capacity by properly controlling martensite volume fraction in dual- phase alloys.     

The role of plastic deformation in the creation of high strength in hard magnetic alloys Fe-Cr-Co-W-Ga

The influence of plastic deformation preceding low-temperature aging on the structural factors that determine the strengthening of the Fe-15Cr-13Co-8W-0.5Ga and Fe-22Cr-l5Co-9W-0.5Ga alloys has been studied. The reasons are discussed for the necessity of employment of different strains to achieve the high-strength state in alloys with different contents of chromium and cobalt.     

Metallography and partitioning of alloying elements in dual-phase steels

The microstructure and the partitioning of alloying elements in dual-phase steels have been studied by conventional and analytical transmission electron microscopy. Systems of compositions Fe-0.15C-1.45Si-0.03Nb (base + Nb), Fe-0.15C-1.45Si-0.38Mo (base + Mo), Fe-0.1C-2Si and Fe-0.1C-0.5Mn were studied. Fine plate precipitates were found in the ferrite phase of all these alloys. The plates are typically 13 nm in diameter and less than 2.5 nm thick, and are oriented on or within a few degrees of the (100) planes. Their density may vary with martensitic volume fraction as well as with the composition of the alloys, and they may have a pronounced effect on thermal and mechanical properties.There is no preferential partitioning of Si to either the ferrite or martensite phases. However, the Si concentration in the ferrite phase has been observed to drop near the ferritemartensite interface, resulting in reduced temper resistance in these regions. Coarse cementite has also been identified in the Fe-0.1C-0.5Mn alloy be electron energy loss spectroscopy.     

On structure property correlation in high strength tungsten heavy alloys

Detailed structure-property correlation has been carried out in high strength tungsten heavy alloys. Alloys of compositions 90W-6Ni-2Fe-2Co, 89W-6Ni-2Fe-3Co, 89.5W-6Ni-2Fe-2Co-0.5Mo, 89.75W-6Ni-2Fe-2Co-0.25Mo, 90W-6Ni-1.5Fe-2.5Co and 90W-6Ni-1Fe-3Co have been prepared by liquid phase sintering followed by large deformation during thermo mechanical processing and studied for microstructure and mechanical properties. Despite differences in composition, higher volume fraction of matrix and lower W-W contiguity in the microstructure result in superior tensile strength and impact toughness. Increasing W content in the matrix enhances mechanical properties by imparting solid solution strengthening, increasing the matrix volume fraction and reducing W-W contiguity. The alloy 90W-6Ni-1Fe-3Co shows superior balance of properties with ultimate tensile strength of 1600 MPa and average impact toughness of 121 J/cm².     

控制第二相方向性析出对铁基合金记忆效应的影响

研究了直接时效和形变时效对Fe-13．53Mn-4．86Si-8．16Cr-3．82Ni-0．16C合金第二相析出、马氏体相变和形状记忆效应的影响．SEM和XRD分析表明,时效后有大量Cr23C6第二相析出,但直接时效析出的Cr23Ca无方向性,而形变时效后Cr23C6呈方向性析出．相同时效时间下,形变时效析出的Cr23C6数量显著增多,且尺寸减小．两种时效均都能显著提高合金的形状记忆效应,且都存在一个最佳的时效时间．形变时效后的形状记忆效应达到82％,显著高于直接时效的记忆效应（43％）．通过控制第二相方向性析出,可制备出不需训练的高形变回复能力的铁基形状记忆合金．     

Martensitic transformation and magnetic properties of Ti-doped NiCoMnSn shape memory alloy

Martensitic transformation, microstructure, and magnetic properties of Ti-doped Ni43-xTixCo7Mn43Sn7（at%）（x = 0, 0.5, 1.0, 2.0, and 4.0） shape memory alloys were investigated. The results show that transformation temperatures of Ni43Co7Mn43Sn7 can be efficiently adjusted by the substitution of Ti for Ni. For example, the martensitic transformation starting temperature（Ms） is reduced by about 278 K with 4 at% addition of Ti. Room temperature microstructure evolves from single tetragonal martensite for the Ti-free alloy to dual phases（tetragonal martensite ＋ second phase） with 0.5 at%, 1.0 at%, and2.0 at% addition of Ti to dual phases（cubic austenite ＋ second phase） for 4.0 at% Ti-doped alloy. The mechanical properties can be obviously improved by adding an appropriate amount of Ti. A noteworthy point is that magnetic-field-induced reverse transformation is observed in Ni39Ti4Co7Mn43Sn7 alloy.     

Role of chromium on mechanical properties of Fe-Mn-Ni-Mo-Ti maraging steels

This experiment investigated the role of chromium in the mechanical properties of Fe-5Mn-9Ni-5Mo-1.5Ti maraging steels containing up to 3% chromium. Remarkable age-hardening responses were observed in the Fe-5Mn-9Ni-5Mo-1.5Ti and Cr-bcaring alloys. A ductile-brittle-ductile transition occurred in the Cr-bearing alloys during isothermal aging below 510°C. This was due to the segregation of titanium and manganese to prior austenite grain boundaries and their subsequent desegregation into the matrix. The addition of chromium to the base alloy considerably improved its ductility after aging at 520°C. From microstructure and AES analyses, it is suggested that chromium addition augments the volume fractions of (Fe,Mn)₂Mo and η-Ni₃Ti precipitates in the Fe-5Mn-9Ni-5Mo-Cr alloys, which act as sinks of manganese and titanium in the matrices. This resulted in the reduction of the alloying elements concentration in the matrix, which is followed by the reduction in the segregation level of the elements at prior austenite grain boundaries, and consequently enhanced intergranular fracture strength. The optimum combination of strength and ductility was obtained in the Fe-5Mn-9Ni-5Mo-3Cr-l.5Ti alloy aged at 520°C for 2 hr. and was σ_{0 2}=1721 MPa, σ_LS=1756 MPa. and ε,= 10.2%.     

Microstructure and mechanical properties of mechanically alloyed and spark plasma sintered amorphous–nanocrystalline Al65Cu20Ti15 intermetallic matrix composite reinforced with TiO2 nanoparticles

Multiphase Al₆₅Cu₂₀Ti₁₅ intermetallic alloy matrix composite, dispersed with 10 wt.% of TiO₂ nanoparticles, has been processed by mechanical alloying, followed by spark plasma sintering under pressure in the temperature range of 623–873 K. Differential scanning calorimetry and X-ray diffraction suggest that equilibrium crystalline phases evolve from the amorphous or intermediate crystalline phases. Transmission electron microscopy shows that the composite sintered at 873 K has partially amorphous microstructure, with dispersion of equilibrium, crystalline, intermetallic precipitates of Al₅CuTi₂, Al₃Ti, and Al₂Cu of 25–50 nm size, besides the TiO₂. The composite sintered at 873 K exhibits little porosity, hardness of 5.6 GPa, indentation fracture toughness in the range of 3.1–4.2 MPa√m, and compressive strength of 1.1 GPa. Indentation crack deflection by TiO₂ particle aggregates causes increase in fracture resistance with crack length, and suggests R-curve type behaviour. The study provides guidelines for processing high strength amorphous–nanocrystalline intermetallic composites based on the Al–Cu–Ti ternary system.     

固溶处理及时效对镍钛形状记忆合金组织演化及力学性能的影响

将镍钛形状记忆合金Ni50.9Ti49.1（摩尔分数）在1123 K固溶处理2 h,然后分别在573、723和873 K时效2h。采用透射电镜、高分辨率透射电镜、扫描电镜和压缩实验,系统研究固溶处理和时效对镍钛合金组织演化及力学性能的影响。结果表明：固溶处理有助于消除原始镍钛样品中的Ti2Ni相,但不能消除TiC相。固溶处理导致镍钛合金中原子排列的有序畴界。在所有时效镍钛样品中,Ni4Ti3析出相、R相和B2奥氏体相共存于室温下的镍钛基体上,然而在873 K时效的镍钛样品中,可以观察到马氏体孪晶。在573和723 K时效的镍钛样品中,细小密集的Ni4Ti3相均匀分布在镍钛基体上,而且与B2基体保持共格关系。然而,在873 K时效的镍钛样品中, Ni4Ti3相尺寸非常不均匀,和B2基体保持共格、半共格和非共格关系。在723 K时效的条件下,细小均匀的Ni4Ti3相阻碍位错运动,导致最大的位错滑移临界分切应力,因此镍钛样品表现出最高的屈服强度。     

Al-Zn-Mg-Cu合金多尺度第二相粒子与性能关系研究

介绍了Al-Zn-Mg-Cu合金多尺度第二相粒子与性能关系的研究。涉及的多尺度第二相粒子包括微米尺度的金属间化合物、亚微米尺度的弥散相、纳米尺度的晶内析出相和晶界析出相;涉及的相关性能为强度、断裂韧性以及腐蚀性能。结合相关文献与作者的研究工作,可以得出以下结论:金属间化合物会影响合金的断裂韧性和腐蚀抗力;弥散相通过抑制基体再结晶的方式影响合金的强度、断裂韧性以及腐蚀抗力;晶界析出相会影响合金的断裂韧性和腐蚀抗力;晶内析出相影响合金的强度和断裂韧性。     

Phase composition and hardening of steels of the Fe-Cr-Ni-Co-Mo system with martensite-austenite structure

The phase composition and mechanical properties of maraging steels of the Fe-Cr-Ni-Co-Mo system are studied as a function of the alloying and of the temperatures of quenching and aging. The intermetallic phases strengthening martensite in different aging stages are determined. The degree of the hardening and the variation of the impact toughness at cryogenic temperatures are compared for steels with different structures (martensite and martensite-austenite) in the stages of maximum hardening and overaging. The effect of retained and reverted austenite on the resistance to crack propagation under impact loading is determined for steels with martensite of a different nature and amount of hardening phases. __________ Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 4, pp. 32–37, April, 2007.     

热处理对12Ni无钴马氏体时效钢微观组织和性能的影响

研究了高温固溶和时效热处理对12Ni无钴马氏体时效钢微观组织和性能的影响。结果表明:在原始固溶态试样中存在粒状和长粒状析出相,经能谱分析为Fe(Mo,Ti)或Fe2Ti型金属间化合物,消耗了大量的强化元素Mo,导致合金时效处理后强度不足(1100MPa);高温固溶处理后消除了粗大析出相,获得单一的板条马氏体组织;进一步改进时效热处理工艺,合金组织呈现弥散分布的纳米尺度的Ni3Mo、Ni3Ti强化相,使合金强度显著提高,达到1225MPa。     

The pitting corrosion of sputtered Fe base alloy films

Predominantly single phase Fe base alloy films were prepared by a DC sputtering method. The compositions of the alloy films, as determined by Auger electron spectroscopy (AES) were Fe-7 at% Cr and Fe-18 at% Cr, Fe-11 at% W and Fe-19 at% W, Fe-9, −13 and −27 at% Ta. The pitting potential of the sputtered alloys determined in chloride solutions was found to be strongly dependent on the nature and the concentration of the alloying element. The pitting potential of sputtered Fe-18 at% Cr and Fe-27 at% Ta alloy films were approximately 0.9 V higher than that of bulk Fe and 0.6 V higher than that of Fe-19 at% W alloy film. A very good correlation was found between the pitting potential of Fe alloy films and the solubility of an alloying element oxide in acidic solutions with a pH corresponding to that within the stable pits of pure Fe (pH = 2). The pitting potential of the Fe alloy was found to increase with a decrease in the solubility of the alloying element oxide in acidic solutions. The pitting potentials of the sputtered Fe-7 at% Cr and Fe-18 at% Cr alloy films were were significantly higher than those of the bulk materials with the same composition. The higher pitting potentials of these alloy films are tentatively attributed to the presence of very fine particles of the oxide phase that are homogeneously distributed in the sputtered alloys.     

Grain refinement of W-Ni-Fe heavy alloys by tantalum element adding

90W-TNi-3Fe and (90-x)W-xTa-7Ni-3Fe (x= 1,3,5,7,10) specimens were attained by liquid phase sintering. A model describing the process of liquid forming and spreading was proposed to point out the differences between alloys doped with tantalum and traditional tungsten heavy alloys. Tantalum priority of entering matrix and a relative high solubility in liquid matrix depress tungsten solubility in liquid matrix, which decreases kinetic rate constant K and consequently results in the reduction of W grain size. The grain refinement is influenced by Ta content and becomes more obvious when Ta content is over 5%. The sample with less than 3%Ta has dominant W and matrix phases. While besides W and matrix phases, intermetallic phases emerge in 85W-5Tai-TNi-3Fe sample. Ta is superfluous and forms a new tantalum phase when more than 7% Ta is added into alloys.     

The influence of hot deformation on the microstructure of Ni-Al and Ni-Al-Fe alloys with small Ti2B addition

Results of microstructure investigation of Ni-Al and Ni-Al-Fe alloys with addition of 0.5at.% Ti₂B after hot deformation are presented. Ti partially dissolves in the matrix, promoting formation of a discontinuous phase and precipitates of γ′ phase of Ll₂ structure during hot deformation of Ni-Al and Ni-Al-4.3at.%Fe alloys. In all investigated alloys precipitates of different compositions, enriched in Ti, were noticed. A compression test proved that due to the grain boundaries strengthening, the fracture mechanism changes into a transcrystalline one, improving fracture toughness of the hot deformed alloy. Fracture occurs in the deformation induced Ll₀ martensite.     

Dynamic Precipitation of Laves Phase and Grain Boundary Features in Warm Deformed FeCrAl Alloy:Effect of Zr

Warm compression deformation of Fe-13.5％Cr-4.7％Al-2.0％Mo-0.70％Nb-0.40Ta (wt％) (FeCrAl) and Fe-13.5％Cr-4.7％Al-2.0％Mo-0.45％Nb-0.40Ta-0.11Zr (wt％) (FeCrAl-Zr) ferritic stainless steel was performed by a thermal simulation machine Gleeble 3800 at 600 ℃ and strain rates of 0.01-10 s-1.Before deformation,all the samples were solution-annealed for 2 h at 1150 ℃ for FeCrAl alloy and 1250 ℃ for FeCrAl-Zr alloy.The strain rate has little or no effect on peak stress,and the precipitates in matrix or grain boundary precipitates (GBPs) have no difference in the samples deformed at the strain rate 0.01 s-1 and 1 s-1 both in FeCrAl and FeCrAl-Zr alloys.The addition of Zr increased the proportion of low-angle grain boundaries (LAGBs).The Laves phase in FeCrAl alloy precipitated uniform in the matrix,while in FeCrAl-Zr alloy Laves phase precipitated at grain boundary and formed GBP.The LAGBs and ∑3 coincident site lattice (CSL) grain boundary both increased in FeCrAl-Zr alloy,which possessed some beneficial properties such as high-temperature creep resistance to the Fe-Cr-Al alloy.More interesting,twins were created by warm deformation,which was difficult in typical bcc ferrite alloy.These results could be expected to provide guidance for subsequent warm working processes for the alloy.     

形变时效温度对Fe-Mn-Si-Cr-Ni合金形状记忆效应的影响

研究了直接时效和形变时效温度对Fe-13Mn-5Si-8Cr-4Ni-0.2C合金形状记忆效应和微观组织的影响.结果表明,直接时效后Fe-Mn-Si-Cr-Ni合金在奥氏体晶界和晶内只有少量Cr23C6第二相弥散析出,而形变后再时效有大量的Cr23C6在奥氏体晶内沿某些特定的方向析出,显著强化基体的同时提高了ε马氏体的可逆逆转变性.形变时效温度影响第二相的析出数量和方向性,从而影响合金的形状记忆效应,存在一个最佳的时效温度.当形变后在1073 K时效300 min时,不仅第二相数量多且在晶内析出的方向性好,合金的形状记忆效应达到89%.     

Experimental Investigation of Phase Equilibria in the Cu-Co-Zr System

Through alloy sampling approach, phase equilibria in the Cu-Co-Zr ternary system have been determined. Based on the phases identified with electron probe microanalysis and x-ray diffraction, isothermal sections at both 873 and 1200 K were constructed. No ternary compound was detected. It is evident that remarkable ternary solubility occurs in almost all binary intermetallic phases at both temperatures. For instance, solubility of Co in Cu₅₁Zr₁₄ can be up to 17.6 and 27.5 at.% at 873 and 1200 K, respectively. Besides, continuous dissolution between CuZr and CoZr at 1200 K was observed, and the maximum content of Cu in CoZr at 873 K reaches to 42.5 at.%.     

Identification and analysis of intermetallic phases in overaged Zr-containing and Cr-containing Al-Zn-Mg-Cu alloys

This paper investigates the effect of alloying elements on the characteristics of intermetallic phases in Zr-containing and Cr-containing 7xxx Al-Zn-Mg-Cu alloys at overaged conditions. Four Al-Zn-Mg-Cu alloy plates with different alloying element contents were studied by optical microscopy based image analysis, differential scanning calorimetry, scanning electron microscopy combined with energy disperse X-ray spectroscopy and transmission electron microscopy. The grain structures, recrystallisation, intermetallic phases and precipitates in the selected alloys have been analyzed and the presence of coarse intermetallic phases has been interpreted using established phase diagrams. The different effects of Zr or Cr addition to the alloys have been compared. The experimental results showed that the recrystallised area fraction of Zr-containing alloys is less than that of Cr-containing alloys, being attributable to Zr reducing recrystallisation more effectively than Cr. The detected particles are mainly S phase, Al₇Cu₂Fe, as well as dispersoids of Al₃Zr for Zr-containing alloys and Cr-rich E phase for Cr-containing alloys. These coarse particles, especially the S phase which cannot be dissolved during solution treatment, are detrimental to the fracture toughness of the alloys.