Influence of isothermal aging onσprecipitation in super duplex stainless steel

The time-temperature-transformation （TTT） curve of the 00Cr25Ni7Mo4N duplex stainless steel was obtained with a Formastor-digital thermal dilatometer, and the influence of isothermal aging on o precipitation was studied by metallographic observation, X-ray diffraction （XRD）, and transmission electron microscopy （TEM）. The results show that the decomposition of ferrite phase is accompanied by the formation of σ phase at 750-1000℃, especially in the range of 800-900℃. The longer the aging time, the higher the amount of o precipi- tation. The area fxaction of various phases remains at a certain value upon the completion of ferrite deformation. The temperature of 850℃ is the most sensitive transaction temperature, the incubation time for the formation of o precipitation is less than 1 min, and aging for 20 min leads to the complete transformation of ferrite. The o phase is formed preferentially at the α/α/γjunction, and then grows along the α/α boundary in the matrix.

Effect of electromigration and isothermal aging on interfacial microstructure and tensile fracture behavior of SAC305/Cu solder joint

The Cu/Sn-3. OAg-0.5Cu/Cu butting solder joints were fabricated to investigate the evolution of the interfacial intertnetaUic compound （ IMC ） and the degradation of the tensile strength of solder joints under the effect of electromigration （ EM） and aging processes. Scanning electron microscopy（SEM） results indicated that the Cu6Sn5 interfacial IMC presented obvious asymmetrical growth with the increase of EM time under current density of l. 78 × 10^4 A/cm^2 at 100 ℃ , and the growth of anodic IMC presented a parabolic relationship with time while the cathodic IMC got thinner gradually. However, as for aging samples at 100℃ without current stressing, the Cu6Sn5 IMC presented a symmetrical growth with a slower rate than the anodic IMC of EM samples. The tensile results indicated that the tensile strength of the solder joints under current stress declined more drastic with time than the aging samples, and the fracture mode transformed from ductile fracture to brittle fracture quickly while the fracture mode of aging samples transformed from cup-cone shaped fracture to microporous gathering fracture in a slow way.

Isothermal Aging Kinetics in CuZnAl Shape Memory Alloy

Isothermal aging behaviours of a CuZnAl shape memory alloy have been investigated by means of dilatometry.The length of the specimens during isothermal aging from 190 to 280℃ increases with the aging time at each temperature.The isothermal aging kinetics fits in Avrami equation and the time exponent n decreases with the increase in aging temperature.The apparent activation energy for the isothermal aging process was measured to be 109.0kJ/mol,which is about equal to that of a relaxation internal friction peak at about 200℃ (f≈1 Hz) in the alloy.

Electrical conductivity changes of bulk tin and Sn-3.0Ag-0.5Cu in bulk and in joints during isothermal aging

The changes of electrical conductivity （resistance） between Sn-3.0Ag-0.5Cu solder joints and printed circuit board （PCB） assembly during aging at 125℃ were investigated by the four-point probe technique. The microstructural characterizations of interfacial layers between the solder matrix and the substrate were examined by optical microscopy and scanning electronic microscopy. Different types of specimens were designed to consider several factors. The experimental results indicate that electrical conductivities （resistances） and residual shear strengths of the solder joint specimens significantly decrease after 1000 h during isothermal aging. Microcracks generate in the solder matrix at the first 250 h. Besides, the evolutions of microstructural characterizations at the interface and the matrix of solder joints were noted in this research.

Precipitates in an isothermally aged Fe-18Cr-12Mn-0.04C-0.48N high-nitrogen austenitic stainless steel

Vertical section of Fe-18Cr-12Mn-0.04C-N system phase diagram varying with nitrogen content at 1×105 Pa was calculated using Thermo-Calc software and thermodynamic database.The morphology and crystallography information of precipitates in Fe-18Cr-12Mn-0.04C-0.48N high-nitrogen austenitic stainless steel during isothermal aging at 800 ℃ after austenization was investigated using optical microscopy(OM),and transmission electron microscopy(TEM) with energy distribution spectrum(EDS).The experimental results show that three precipitates,(Cr,Fe,Mn)2(N,C),(Cr,Fe,Mn)23(C,N)6 and σ phase exist in this steel,which is consistent with the thermodynamic calculation,indicating that thermodynamic calculation can provide instructions for alloy composition design,heat treatment and prediction of precipitation sequence in Fe-18Cr-12Mn-0.04C-N system.

Influence of long-term isothermal aging on microstructure and creep rupture properties of Ni-base superalloy M4706

After a standard heat treatment,the microstructural evolution with time during isothermal aging at 850°C and its effect on the creep rupture properties of the Ni-base superalloy M4706 at 870°C and 370 MPa are investigated.It is found that as the aging time increases from 0 to 5000 h,the average diameter of coarseγ′increases from 241 to 484 nm,and the distribution of the carbides at grain boundaries changes from discontinuous to continuous.Moreover,experimental observations on the microstructures of all the crept specimens reveal that dislocation bypassing controls the creep deformation.Thus,it is concluded that the transitions in the microstructures result in the degeneration of the creep rupture properties of the experimental alloy with aging time.

Microstructure and Shear Properties Evolution of Minor Fe-Doped SAC/Cu Substrate Solder Joint under Isothermal Aging

Different amounts of Fe(0.005,0.01,0.03,0.05,and 0.07 wt%)were added to SAC305 to study the shear behavior damage of Fe-doped SAC solder joints under thermal loading(170℃,holding time of 0,250,500,and 750 h).The results show that during isothermal aging at 170℃,the average shear force of all solder joints decreases with increasing aging time,while the average fracture energy first increases and then decreases,reaching a maximum at 500 h.Minor Fe doping could both increase shear forces and related fracture energy,with the optimum Fe doping amount being 0.03 wt%within the entire aging range.This is because the doping Fe reduces the undercooling of the SAC305 alloy,resulting in the microstructure refining of solder joints.This in turn causes the microstructure changing from network structure(SAC305 joint:eutectic network+β-Sn)to a single matrix structure(0.03Fe-doped SAC305 joint:β-Sn matrix+small compound particles).Specifically,Fe atoms can replace some Cu in Cu_(6)Sn_(5)(both inside the solder joint and at the interface),and then form(Cu,Fe)_(6)Sn_(5) compounds,resulting in an increase in the elastic modulus and nanohardness of the compounds.Moreover,the growth of Cu_(6)Sn_(5) and Cu_(3)Sn intermetallic compounds(IMC)layer are inhibited by Fe doping even after the aging time prolonging,and Fe aggregates near the interface compound to form FeSn_(2).This study is of great significance for controlling the growth of interfacial compounds,stabilizing the microstructures,and providing strengthening strategy for solder joint alloy design.

In-situ isothermal aging TEM analysis of a micro Cu/ENIG/Sn solder joint for flexible interconnects

Sn/ENIG has recently been used in flexible interconnects to form a more stable micron-sized metallurgical joint,due to high power capability which causes solder joints to heat up to 200℃.However,Cu_(6)Sn_(5)which is critical for a microelectronic interconnection,will go through a phase transition at temperatures between 186 and 189℃.This research conducted an in-situ TEM study of a micro Cu/ENIG/Sn solder joint under isothermal aging test and proposed a model to illustrate the mechanism of the microstructural evolution.The results showed that part of the Sn solder reacted with Cu diffused from the electrode to formη´-Cu_(6)Sn_(5)during the ultrasonic bonding process,while the rest of Sn was left and enriched in a region in the solder joint.But the enriched Sn quickly diffused to both sides when the temperature reached 100℃,reacting with the ENIG coating and Cu to form(Ni_(x)Cu_(1-x))_(3)Sn_(4),AuSn_(4),and Cu_(6)Sn_(5)IMCs.After entering the heat preservation process,the diffusion of Cu from the electrode to the joint became more intense,resulting in the formation of Cu_(3)Sn.The scallop-type Cu_(6)Sn_(5)and the seahorse-type Cu_(3)Sn constituted a typical two-layered structure in the solder joint.Most importantly,the transition betweenηandη’was captured near the phase transition temperature for Cu_(6)Sn_(5)during both the heating and cooling process,which was accompanied by a volume shifting,and the transition process was further studied.This research is expected to serve as a reference for the service of micro Cu/ENIG/Sn solder joints in the electronic industry.

Effects of nano-sized Ag reinforcing particulates on the microstructure of Sn-0.7Cu solder joints

Composite solders were prepared by mechanically dispersing different volumes of nano-sized Ag particles into the Sn-0.7Cu eutectic solder. The effects of Ag particle addition on the microstructure of Sn-0.7Cu solder joints were investigated. Besides, the effects of isothermal aging on the microstructural evolution in the interfacial intermetallic compound （IMC） layer of the Sn-0.7Cu solder and the composite solder reinforced with 1vol% Ag particles were analyzed, respectively. Experimental results indicate that the growth rate of the interfacial IMC layer in the Ag particles reinforced composite solder joint is much lower than that in the Sn-0.7Cu solder joint during isothermal aging. The Ag particles reinforced composite solder joint exhibits much lower layer-growth coefficient for the growth of the IMC layer than the corresponding solder joint.

Thermal reliabilities of Sn−0.5Ag−0.7Cu−0.1Al_(2)O_(3)/Cu solder joint

The effects of trace addition of Al_(2)O_(3) nanoparticles(NPs)on thermal reliabilities of Sn−0.5Ag−0.7Cu/Cu solder joints were investigated.Experimental results showed that trace addition of Al_(2)O_(3) NPs could increase the isotheraml aging(IA)and thermal cyclic(TC)lifetimes of Sn−0.5Ag−0.7Cu/Cu joint from 662 to 787 h,and from 1597 to 1824 cycles,respectively.Also,trace addition of Al_(2)O_(3) NPs could slow down the shear force reduction of solder joint during thermal services,which was attributed to the pinning effect of Al_(2)O_(3) NPs on hindering the growth of grains and interfacial intermetallic compounds(IMCs).Theoretically,the growth coefficients of interfacial IMCs in IA process were calculated to be decreased from 1.61×10^(−10 )to 0.79×10^(−10) cm^(2)/h in IA process,and from 0.92×10^(−10) to 0.53×10^(−10) cm^(2)/h in TC process.This indicated that trace addition of Al_(2)O_(3) NPs can improve both IA and TC reliabilities of Sn−0.5Ag−0.7Cu/Cu joint,and a little more obvious in IA reliability.

A simple method of synthesizing multi-wall carbon nanotubes/SnO core/shell nanostructure

Multi-wall carbon nanotubes(MWNTs)/SnO core/shell nanosturcture was synthesized by a simple solution-based method,in which SnCl2 was solved in distilled water containing dispersed MWNTs,then stired,filtered and washed in ambient atmosphere,finally dryed in air at 90 ℃ for 6 h.The MWNTs/SnO core/shell nanostructure was characterized by X-ray diffraction(XRD),transmission electron microscopy(TEM).It is found that surface defects of MWNTs are necessary for the deposition of SnO.The mechanism of the SnO nanocoating formation through the hydrolysis of SnCl2 in water(4SnCl_2+2H_2O-Sn_4(OH)2Cl_6+2HCl) was presented.

Microstructure and shear properties evolution of Mn-doped SAC solder joint under isothermal aging

The effects of Mn addition(0.005,0.01,0.03,0.05,and 0.07 wt.%)on microstructure,shear mechanical behavior,and interfacial thermal stabilities of SAC305 joints were investigated under isothermal aging temperatures of 170 C with different aging time(0,250,500,and 750 h).It is found that Mn addition can increase fracture energy of joints without decreasing the shear strength.And the microstructures have transformed from the eutectic net-like structure in SAC305 solder joints into the structures based onβ-Sn matrix with intermetallic compounds(IMCs)distributed.By doping 0.07 wt.%Mn,the Cu_(6)Sn_(5) growth along the SAC305/Cu interface during thermal aging can be inhibited to some extent.During isothermal aging at 170°C,the maximum shear force of solder joint decreases continuously with aging time increasing,while the fracture energy rises first and then decreases,reaching the maximum at 500 h compared by that with the microstructure homogenization.Cu_(3)Sn growth between Cu_(3)Sn_(5)/Cu interface has been retarded most at the aging time of 250 h with 0.07 wt.%Mn-doped joints.With the aging time prolonging,the inhibition effect of Mn on CusSn IMC layer becomes worse.The strengthening effect of Mn can be explained by precipitation strengthening,and its mechanical behavior can be predicted by particle strengthening model proposed by Orowan.

Microstructures and mechanical properties of homogenization and isothermal aging Mg–Gd–Er–Zn–Zr alloy

The effects of homogenization and isothermal aging treatment on the mechanical properties of Mg-12Gd- 2Er-1Zn-0.6Zr （wt%） alloy were investigated. The precipitated long-period stacking order （LPSO） structure and the aging precipitation sequence of the conditioned alloys were observed and analyzed, respectively. The results indicate that the 14H-LPSO structure occurs after the homogenization treatment and the 131 phase forms after the isothermal aging process. These two independent processes could be controlled by the precipitation temperature range. The significant increase in the elongation of the as-cast alloy after homogenization treatment is attributed to the disappearance of the coarse primary Mgs（Gd, Er, Zn） phase and the presence of the 14H-LPSO structure. The precipitation sequence of the investigated alloy is α-Mg（SSS）/β″（D019）/β′（cbco）/β. Furthermore, the yield tensile strength （YTS） and ultimate tensile strength （UTS） values of the isothermal aging alloy have a great improvement, which could be attributed to the high density of the precipitated β′ phase.

Correlation between precipitates evolution and mechanical properties of Al-Sc-Zr alloy with Er additions

Correlation between precipitates evolution and mechanical properties of Al-Sc-Zr alloy with Er additions during isothermal ageing were investigated by microhardness measurements,transmission electron microscopy,atom probe tomography and density functional theory-based simulations.The results demonstrate that the Er additions significantly improve the hardness during elevated temperature ageing,especially at 400℃.This is mainly because Er additions increase the nucleation rate of the Al_(3)(Er,Sc,Zr)precipitates,resulting in a higher density of fine and uniform dispersion of L1_(2)structured nanoparticles.First-principles calculations demonstrate that the second nearest neighboring solute-solute interactions for the species Sc,Zr and Er are energetically favored–a key feature to rationalize the observed precipitate structure and the underlying formation mechanism.The sequential formation of the core/shell precipitates in the Er-free alloy and core/double-shell precipitates in the Er-containing alloy arises due to the different solute-solute and solute-vacancy interaction energies,and the relative diffusivities of the Er,Sc and Zr species in Al.These results shed light on the beneficial effects of Er additions on the agehardening behavior of Al-Sc-Zr alloy and provide guidance for designing the ageing treatments for the Al-Sc-Zr(-Er)alloys.

Precipitation Kinetics of Cr_2N in High Nitrogen Austenitic Stainless Steel

The precipitation behavior of Cr2 N during isothermal aging in the temperature range from 700 ℃ to 950 ℃ in Fe-18Cr-12Mn-0.48N （in mass percent） high nitrogen austenitic stainless steel, including morphology and content of precipitate, was investigated using optical microscopy, scanning electron microscopy, and transmission electron microscopy. The isothermal precipitation kinetics curve of Cr2 N and the corresponding precipitation activation energy were obtained. The results show that Cr2N phase precipitates in a cellular way and its morphology is transformed from initial granular precipitates to lamellar ones in the cell with increasing aging time. The nose temperature of Cr2 N precipitation is about 800 ℃, with a corresponding incubation period of 30 min, and the ceiling temperature of Cr2N precipitation is 950℃. The diffusionactivation energy of Cr2 N precipitation is 296 kJ/mol.

Effects of Mo on the Precipitation Behaviors in High-Nitrogen Austenitic Stainless Steels

Precipitation behaviors of Fe-18Cr-18Mn-0.63N and Fe-18Cr-18Mn-2Mo-0.69N high-nitrogen austenitic stainless steels during isothermally aging at 850℃ have been investigated by optical microscopy （OM）, scan- ning electron microscopy （SEM）, transmission electron microscopy （TEM） and X-ray diffraction （XRD）. The experimental results show that precipitation displays a discontinuous cellular way and the precipitates are identified as Cr2N in Fe-18Cr-18Mn-0.63N steel. The addition of Mo makes precipitation occur not only at the grain boundary but also inside the grain and precipitation also displays discontinuous cellular way. The precipitates at the grain boundary and in the cell are both identified as Cr2N phase and X phase and the precipitates inside the grain are identified as X phase in Fe-18Cr-18Mn-2Mo-0.69N steel. The nucleations of X phase and Cr2N phase at the grain boundary are both governed by the diffusion of Cr atoms. The formation and growth of X phase inside the grain are induced by the impoverishment of N atoms with increasing aging time.

Influence of External Interface Normal Stress on the Growth of Cu-Sn IMC During Aging

A U-shape clamp was designed to apply stress perpendicular to the interface of Cu/Sn/Cu solder joints,and its influence on the growth behavior of Cu-Sn intermetallic compound(IMC)during thermal aging at 150℃ was investigated.The results show that compared with the sample at general stress-free state,the growth rate of IMC under compression is faster,while that under tension is slower.Moreover,the interface between IMC and Sn is smoother under compressive stress,and the corresponding IMC grains are smaller and more uniform than that under tensile stress.According to the growth kinetic analysis,the growth of IMC under general,compressive and tensile states is all controlled by the combination of grain boundary diffusion and volume diffusion with a similar growth exponent(n≈0.4).However,external stress can affect the Ostwald ripening process of grain growth,causing a change of grain size and grain boundary density in the IMC layer.As a result,the IMC growth behavior at the interface of the solder joint will be affected by the applied external normal stress.