工艺管线焊后热处理脱层的原因分析及对策

对中国石油集团济柴动力总厂成都压缩机厂某压缩机组的工艺气管线的焊后热处理脱层进行了原因分析,制定出有效措施,保证了工艺管线焊后热处理质量。

Intermetallic phase evolution of 5059 aluminum alloy during homogenization

Intermetallic phase evolution of 5059 aluminum alloy during homogenization was investigated by means of optical microscopy （OM）, scanning electron microscopy （SEM）, transmission electron microscopy （TEM）, energy dispersive spectrometry （EDS）, differential scanning calorimetry （DSC） and X-ray diffraction analysis （XRD）. The results show that severe dendritic segregation exists in as-cast alloy. The dissolvable intermetallic phases in as-cast alloy consist of Zn-and Cu-rich non-equilibriumβ（Al3Mg2） phase, Fe-rich eutectic Al6Mn phase and equilibrium Mg2Si phase. During the homogenization, Zn- and Cu-rich non-equilibrium β （Al3Mg2） phase, Fe-rich eutectic Al6Mn phase and equilibrium Mg2Si gradually dissolve into matrix. Fine dispersed β（Al3Mg2） particles and rod-shaped Al6Mn particles form in the Al matrix after homogenization. The proper homogenization processing is at 450 °C for 24 h, which is consistent with the results of homogenizing kinetic analysis.

Microstructural evolution of AZ91 magnesium alloy during extrusion and heat treatment

Microstructural evolution of AZ91 magnesium alloy was investigated during homogenizing annealing treatment, hot extrusion and ageing treatment, respectively. The results exhibited that both the divorced eutectic β-Mg17Al12 and the precipitated β-Mg17Al12 phases appeared in the as-cast alloy. The β-Mg17Al12 phase dissolved into α-Mg matrix mostly and the structure kept fine after the optimized homogenization treatment at 380 °C for 15 h. Dynamic recrystallization and consequent grain refinement occurred during extrusion. The banded β-Mg17Al12 precipitates paralleled to the extrusion direction were observed after ageing treatment. The banded precipitation should be attributed to the solidification segregation which was elongated during the subsequent extrusion. Furthermore, the effects of temperature, holding time of homogenization and ageing treatment, and extrusion processing parameters on the microstructural evolution of AZ91 alloy were also discussed in details according to the experimental results.

Influence of Ni_4Ti_3 precipitates on phase transformation of NiTi shape memory alloy

Ni Ti shape memory alloy samples were aged for 2 h at 573, 723 and 873 K, respectively. Two R-phase variants are observed in the Ni Ti samples aged at 573 and 723 K, where the orientation relationship between the two R-phase variants and the B2 matrix is determined. In the Ni Ti samples aged at 573 and 723 K, fine and homogeneous Ni4Ti3 precipitates are coherent with the B2 austenite matrix. The Ni4Ti3 particles precipitate in the grain interior and at the grain boundaries, where the heterogeneous Ni4Ti3 precipitates are coherent, semi-coherent and incoherent with the B2 matrix in the Ni Ti sample aged at 873 K. As for the Ni Ti sample aged at 873 K, one-stage phase transformation from B19＇ martensite to B2 austenite occurs on heating, but two-stage phase transformation of B2-R-B19＇ arises on cooling. The Ni Ti sample aged at 723 K shows two-stage phase transformation of B2-R-B19＇ on cooling as well, but exhibits two-stage phase transformation of B19＇-R-B2 on heating. The Ni Ti sample aged at 573 K exhibits three-stage transformation on cooling due to local stress inhomogeneity and local composition inhomogeneity around the Ni4Ti3 precipitates.

Structure and properties of FeCoNiCrCu_(0.5)Al_x high-entropy alloy

Effects of Al content and heat treatment on the structure,hardness and electrochemical properties of FeCoNiCrCu0.5Alx high-entropy alloys were investigated.The phase structure of as-cast alloys evolves from FCC phase to BCC phase with the increase of Al content.The stable phase of FeCoNiCrCu0.5Alx high-entropy alloys will transform from FCC phase to FCC＋BCC duplex phases when x value increases from 0.5 to 1.5.The hardness of BCC phase is higher than that of FCC phase,and the corrosion resistance of BCC phase is better than FCC phase in chlorine ion and acid medium.High hardness and good corrosion resistance can be obtained in as-cast FeCoNiCrCu0.5Al1.0 alloy.

Effect of Ce,Co,B on formation of LaCo_(13)-structure phase in La(Fe,Si)_(13) alloys

The effect of Ce, Co, and B on the formation of 1：13 phase in La（Fe, Si）13 alloys was investigated by XRD, SEM and EDS. The results show that Co can improve the formation of 1：13 phase in as-cast LaFe11.6-xCoxSi1.4 alloys, but in as-cast and annealed LaFe11.6Si1.4-xCox alloys, it will hamper the formation of 1：13 phase and help the formation of a-Fe（Co, Si） solid solution. Ce2Fel7 phases will form when x reaches a certain value in as-cast and annealed La1-xCexFe11.5Si1.5 alloys. B can improve the formation of 1：13 phase accompanied with Fe2B phase in as-cast LaFe11.6-xBxSi1.4 alloys. B improves the formation of a-Fe solid solution in LaFe11.6Si1.4-xBx alloys, and there is almost only a-Fe in as-cast and annealed LaFe11.6Si0.9B0.5 alloy. In all, the introduction of Co, B, and Ce cannot eliminate the a-Fe phases in corresponding alloys prepared by the high-temperature and short-time annealing process.

Microstructure of cast γ-TiAl based alloy solidified from β phase region

The microstructures and phase transformation of Ti-43Al-4Nb alloy in as-cast and heat-treated states were investigated by using optical microscopy, scanning and transmission electron microscopy as well as differential scanning calorimetry. The results show that a fine microstructure of the as-cast alloy can be obtained by solidifying through the β phase. γ grains can nucleate directly from the β phase. The coexistence of β phase and γ phase along primary α grain boundaries contributes to the decrease in the grain size of the as-cast alloy. The phase transformation sequence during solidification of the Ti-43Al-4Nb alloy is suggested as L→L＋β→β→α＋β→α＋βr→α＋γ＋βr→lamellae（α2＋γ）＋γ＋βr. The microstructure of the alloy after heat treatment at 1 250 ℃ for 16 h exhibits a certain coarsening compared with that of the as-cast state. The remnant β phase can be removed by the heat treatment process due to the diffusion of Nb and the non-equilibrium state of β phase.

Microstructure characterization on Mg-2Nd-4Zn-1Zr alloy duringheat treatment

The microstructures of Mg-2Nd-4Zn-1Zr alloy in the as-cast state and after heat treatment were investigated. Several kinds of secondary phases were found and characterized by transmission electron microscopy （TEM）, scanning electron microscopy （SEM） and X-ray diffraction （XRD）. In the as-cast alloy, the existing eutectic compounds are Mg-Nd-Zn ternary phases： T phases and W phases. After the heat treatment, with increasing the temperature or time, it was found that T phase almost dissolved into the α-Mg matrix, while a large amount of W phase remained in the matrix. On the other hand, with prolonging the time, the morphology of the phase changed from continuous network to the spherical shape along the grain boundary. The density of the W phase gradually decreased and finally it was coarsened and stabilized in the treatment process.

神奇的抗菌锅

德国的锅具制造公司研制成功一种天然、无毒、无味并具备抗菌功能的高科技锅，．

Microstructure and mechanical properties of strontium-modified ADC12 alloy processed by heat treatment

The effects of heat treatment and strontium （SO addition on the microstructure and mechanical properties of ADC12 alloys were investigated, and two-stage solution treatment was introduced. The results indicated that the addition of Sr obviously refined the microstructure of ADC12 alloys. When 0.05 wt% Sr was added into the alloy, the eutectic Si phase was fully modified into fine fibrous structure; a-A1 and fl-A15FeSi phases were best refined; and the eutectic AlzCu phase was modified into block-like AlzCu phase that continuously distributed at the grain boundary. The ultimate tensile strength （UTS） （270.63 MPa） and elongation （3.19%） were increased by 51.2% and 73.4% respectively compared with unmodified alloys. After the two-stage solution treatment （500 ~C, 6 h＋520 ~C, 4 h）, for 0.05 wt% Sr modified ADC12 alloys, the Si phases transformed into fine particle structure and AlzCu phases were fully dissolved. The peak hardness value of the alloys processed by the two-stage solution treatment was increased by 8.3% and 6.8% respectively compared to solution treatment at 500 ~C and 520 ~C. After the aging treatment （175 ~C, 7 h）, the hardness and UTS were increased by 38.73% and 13.96% respectively when compared with the unmodified alloy.

Mechanical alloying and subsequent heat treatment of Ag-Zn powders

Microstructural evolution during mechanical alloying of Ag and Zn, and subsequent heat treatments were investigated. The mechanical alloying was carried out in a SPEX 8000D miller. The microstructural characterization was obtained by X-ray diffraction （XRD）, transmission electron microscopy （TEM） and scanning electron microscopy （SEM）. The thermal behavior was studied using differential scanning calorimetry （DSC）. Based on the results obtained, it can be concluded that at the early stages of milling was possible to detect the ε, β, β′, α solid solutions and remaining Zn. Later, the ε, β, β′ and Zn phases disappeared while the Zn concentration of the α solid solution was strongly increased. After 7.2 ks of milling, the mechanical alloying process reached a steady state. During this period, both the composition and crystallite size of the α solid solution remained practically unchanged. On the other hand, subsequent heat treatments of milled powders showed that the α solid solution could also be obtained by the combination of mechanical alloying and heat treatment. Finally, the evolution of the microstructure during milling and annealing was combined to propose an optimal processing route in order to obtain a α solid solution.

Influence of heat treatment on microstructure and electrochemical behaviors of Mg-Zn binary alloys prepared by gas-phase alloying technique

Mg-Zn binary alloys fabricated by the gas-phase alloying technique under vacuum condition were investigated in the state of initial state and after heat treatment for the microstructure and electrochemical behaviors.Different from the traditional Mg-Zn alloys preparation methods,alloys prepared by gas-phase alloying have a large number of intermetallic compounds,such as MgZn,Mg7Zn3 and MgZn2.After solution treatment,the boundary of the eutectic disappeared and the size ofα-Mg increased from 100μm to 150μm.At the same time,the value of the resistance of charge transfer increased,which indicates that the resistance of the charge transfer and the corrosion resistance of the alloys increased.After artificial aging treatment,the distribution ofα-Mg was more uniform and its size was reduced to about 50μm,and there was new eutectic structure formed.The newly formed eutectic structure forms galvanic cells with the alloy matrix,which makes the corrosion resistance of the alloy weaken.

Study on Grain Refining and Metamorphism of ZL111 Aluminium Alloys

Vacuum sintering and ball milling methods were employed in the preparation process of Ti-C grain refine- ment and the ability of refiners with varying ratios of Ti and C to refine ZL111 crystal grains was tested. The refinement effect of the Ti-C ratios on tensile strength, elongation percentage, Brinell hardness, pro-eutectoid αAl and the size of the Si phase of ZL111, after modification by rare-earth and strontium nitrate, were studied by means of metallographic examination, SEM and mechanical property tests. The results show that there is an obvious increase in the tensile strength and elongation percentage of refined ZL111 with these new Ti and C refiner compounding powders, while Brinell hardness remained more or less constant. The pro-eutectoid αAl is considerably reduced in size and the Si phase shows a finer and rounder structure. The refiner exhibits a good grain refining performance when the Ti-C ratio is 25:1, for Al crystals can favorably easily form nuclei and grow up along the TiC surface thanks to the TiAl3 generated by sur- plus Ti and Al. The mechanical properties have clearly been improved by the addition of strontium nitrate to ZL111. The effective factors in the modification of mechanical properties of ZL111 are in order of importance: strontium nitrate, Ti-C ratio and rare earth.

Effect of thermal treatment and ball milling on microstructure and phase transformation of Ni-Mn-Ga-Nb alloys

To clarify phase transformation evolution of Nb-doped Ni-Mn-Ga bulk alloys after aging and ball milling, the microstructure and phase transformation of the aged and ball-milled dual-phase Nb-doped Ni-Mn-Ga alloys were investigated by SEM, EDS, XRD, DSC and susceptibility measurements. The as-cast alloys were mainly composed of the second phase with layer-shape and presented a reduced martensitic transformation with increasing the second phase content. The second phase transformed from layer-shape to dense bar-shape and the martensitic transformation was enhanced after being quenched at 1173 K. After aging at 673 and 873 K, the 3% Nb alloy with less second phase exhibited a single-step phase transformation, whereas the 6% Nb and 9% Nb alloys with more second phase exhibited a two-step martensitic transformation and Curie transition. The martensitic transformation and Curie transition of the as-milled dual-phase particles disappeared and were retrieved after annealing at 1073 K due to the recovery of high ordered structure of the matrix.

Effects of annealing at 800 and 1000℃ on phase precipitates and hardness of Al_(7)Cr_(20)Fe_(x)Ni_(73)−x alloys

The effects of Fe content on the microstructure,phase constituents and microhardness of the as-cast,800℃or 1000℃-annealed Al_(7)Cr_(20)Fe_(x)Ni_(73)−x(x=13−66)alloys were investigated.Not all these alloys are composed of the single FCC phase.The BCC and B2 phases are found.It is confirmed that the BCC phase in the Al7Cr20Fe66Ni7 alloy is transformed from the FCC phase at about 900℃ during cooling.While in the 800℃-annealed Al7Cr20Fe60Ni13 alloy,the FCC phase is stable and the hardness decreases.After annealing at 1000℃,for the precipitation of the B2 particles,the Al content in the FCC phase decreases,which results in decreasing of the alloy hardness.Moreover,after annealing at 800℃,a small amount of Al-rich B2 particles precipitate at the phase boundary and some nanocrystal BCC phase precipitates in the FCC matrix,which increases the hardness of the Al_(7)Cr_(20)Fe_(x)Ni_(73)−x(x=41−49)alloys.These results will help to the composition design and processing design of the Al−Cr−Fe−Ni based high-entropy alloys.

Effect of heat treatments on microstructure and mechanical properties of sand cast Al−2Li−2Cu−0.5Mg−0.2Sc−0.2Zr alloy

This study focused on modifying heat treatment schemes to enhance the mechanical properties of sand cast Al−2Li−2Cu−0.5Mg−0.2Sc−0.2Zr alloy.Different three-stage solution treatment schemes((460℃,32 h)+(520℃,24 h)+(530/540/550℃,4/12/24/32 h))and aging temperatures(125,175,225℃)were designed for comparison.The microstructure evolutions were analyzed by optical microscopy(OM),scanning electron microscopy(SEM)and transmission electron microscopy(TEM).The results showed that the three-stage solution treatment of(460℃,32 h)+(520℃,24 h)+(530℃,12 h)could dissolve most of the secondary phases.The TEM results illustrated that fineδ'(Al_(3)Li)particles were homogeneously distributed in the matrix after aging at 175℃for 8 h,accompanied by a small amount of lath-shaped S′(Al_(2)CuMg)and plate-like T_(1)(Al_(2)CuLi)phases.The best comprehensive properties of yield strength of 376 MPa,ultimate tensile strength of 458 MPa and elongation of 4.1%were obtained by the optimal heat treatment scheme((460℃,32 h)+(520℃,24 h)+(530℃,12 h)+(175℃,8 h)).

Effect of Different Sizes of α Phase on Tensile Properties of Metastable β Titanium Alloy Ti-5.5Cr-5Al-4Mo-3Nb-2Zr

To study the relationship between the microstructure and tensile properties of the novel metastable β titanium alloy Ti-5.5Cr-5Al-4Mo-3Nb-2Zr,a heat treatment process of ABFCA(solid solution in α+βregion with subsequent furnace cooling followed by aging treatment finally)was designed,by which α phases of different sizes can be precipitated in the β matrix.The results show that the microstructure obtained by this heat treatment process is composed of primary α(α_(p))phase,submicro rod-like α(α_(r))phase and secondary α(α_(s))phase.The alloy with multi-scale α phase has an excellent balance between strength and ductility.The elongation is about 18.3% at the ultimate tensile strength of 1125.4 MPa.The relationship between the strength of the alloy and the α phase was established.The strength of the alloy is proportional to the power of‒1/2 of the average spacing and width of α phase.The α_(s) phase with a smaller size and phase spacing can greatly improve the strength of the alloy by hindering dislocation slip.The transmission electron microscope analysis shows that there is a large amount of dislocation accumulation at the α/β interfaces,and many deformation twins are found in the α_(p) phase after tensile deformation.When the dislocation slip is hindered,twins occur at the stress concentration location,and twins can initiate some dislocations that are difficult to slip.Meanwhile,the plastic strain is distributed uniformly among the α_(p),α_(r),α_(s) phases and β matrix,thereby enhancing the ductility of the alloy.

Effect of Precipitate Phases and Grain Size on Mechanical Properties of Inconel 718 Superalloy After Various Heat Treatments

Various heat treatments were conducted on Inconel 718 superalloy,and the resultant microstructures and properties were investigated to analyze the mechanisms of heat treatments.Results show that the type and quantity of precipitate phases and the grain size have different effects on the properties of Inconel 718 superalloy after various heat treatments.Theγ"andγ'phases as well as grain size mainly influence the strength,and theδphase mainly influences the plasticity.Besides,the precipitation ofγ"andγ'strengthening phases can improve the yield strength.The alloy strength is inversely proportional to mean grain size when theγ"andγ'phases have similar contents.The plasticity is susceptible to the content and shape ofδphase.A proper amount ofδphase is beneficial to the plasticity,but excessiveδphase degrades plasticity.