during the transition from traditional pb - containing solders to lead - free solders in the electronics industry , sn  ag  cu solders became the industry 's favourite for most applications . however , the melting range of these solders lies around 220  c , which is considerably higher than the previously used ( near ) eutectic pb  sn alloys . several attempts were therefore made to reduce the melting temperature by adding various low melting metals , e.g. ga or in . although basically satisfying results were obtained the industry did not particularly like the idea of adding in due to its high cost and limited availability . nevertheless , in is included in the thermodynamic calphad database solders ,   developed in the scope of the cost action 531  lead - free solder materials  , which was designed to include datasets for all elements that could possibly find use in lead - free soldering for mainstream applications . these efforts were then continued within the scope of cost action mp0602 on high - temperature solders in the form of an expanded database . the aim of this database is to provide reliable phase diagram descriptions for intermetallic systems of the type solder  +  substrate  to allow the understanding and interpretation of interfacial reactions during the soldering process . with calphad being a semi - empirical approach and therefore being strongly dependent on experimental information , it is clear that any useful calphad optimization needs a reliable experimental basis . on the other hand , intermetallic systems of the type solder  +  substrate  are complicated by the huge differences in the melting points of the pure metals . the high melting regions of the system are therefore practically inaccessible by experiments at the temperatures relevant for soldering , i.e. around 200  c . it is therefore necessary to employ both , experiments and modelling , in order to produce the required phase diagram information . due to these reasons , the goal of the present work was the experimental determination of the phase equilibria in the system in sn at 700  c using x - ray diffraction ( xrd ) and scanning electron microscopy ( sem ) including micro probe analysis ( empa ) and energy dispersive x - ray spectroscopy ( edx ) . this particular temperature was chosen because it allows obtaining reliable results in reasonable time . since no theoretical description of the in ni  sn system has been done in the past , the experimental work presented here is complemented by a theoretical study based on the experimental data . as calphad modelling ,   relies on the combination of experimental data and theoretical modelling , its success significantly depends on the amount and quality of available experimental data . as a first result of the modelling efforts experimental phase diagram information on the binary boundary systems was taken from the literature : ni  sn from the recent investigation of schmetterer et  al .   who primarily investigated the high temperature ( ht )  low temperature ( lt ) transitions in ni3sn and ni3sn2 and determined the involved reaction temperatures . information on the in  ni system was in principle taken from the compilation of singleton and nash . in this system the homogeneity ranges of the  and -ni2 in phases are of note . however , the available data were enhanced with a number of own measurements in the binary system , because some inconsistencies between the ternary data and the literature on the binary system were noticed ( see chapter 4 ) . the thermodynamic description of the binary systems was taken from the literature , the solders database ,   and our own assessment work . the source of the thermodynamic parameters for the in  ni system is ref .  . for in  sn the data from ansara et  al .   were selected out of the various assessments ( e.g. , , ) due to their consistency with the unary data in the solders database and good agreement with the experimental version from ref .  . sn dataset was taken from the complete reassessment of this system by zemanova et  al .   which is based on the new experimental results by schmetterer et  al . consistency between the thermodynamic data for the various binary systems in the solders database and the new database for high - temperature lead - free solders ( developed within the scope of cost action mp0602 ) , demanded new models for the intermetallic phases in ni sn , e.g. ni3sn - phase having d03 structure was remodelled as a bcc_a2 structure in order to be consistent with the cu sn system , where bcc- and d03- had been assessed as being one phase for simplicity ( as bcc_a2 ) and with the ternary cu  ni  sn system , where a continuous solubility had been observed between ni3sn ht and  that required this unification of the description . the experimental literature information on the ternary in sn system is partially summarized in . a phase diagram study at 700  c was published by bhargava and schubert , who established a partial isothermal section in the ni - rich part , whereas the ( in , sn)-rich area was investigated using samples that had been furnace - cooled to room temperature . the authors also reported the  existence of a ternary compound inni6sn5 having c2mou - type crystal structure and a complete solid solution between inni2 and  ni3sn2 . another partial isothermal section at 550  c in the range 60100 at.% ni was suggested by burkhardt and schubert . recently huang and chen   proposed isothermal sections at 160 and 240  c within their lead - free solder related research . in contrast to the results by   they did not find any ternary compound , but suggested a huge solubility of in in the ni3sn4-phase , while according to , there is only a limited solubility of in in ni3sn4 at 700  c . another ternary phase , inni2sn , is mentioned in   to be a solid solution of sn in inni , and a cosn - type crystal structure is reported for this phase . a crystallographic study of the ni3(in , sn ) phase was carried out by shadangi et  al .   who reported a continuous solid solution between the isostructural ni3sn and ni3 in phases at 500  c . ni  sn samples were prepared from the pure elements , ni - sheet ( 99.99% , advent research materials ltd . , eynsham , oxford , u.k . ) , sn - ingot ( 99.999% metal basis , ventron alfa products , beverly , ma , usa ) and in - rod ( 99.999% , asarco , south plainfield , nj ) . proper amounts of the elements were weighed to give a total sample weight of 1  g. alloying was done either in an arc furnace or directly in dried and evacuated quartz glass tubes . in both cases , necessary care had to be taken to ensure the homogenization of the samples due to the very slow reaction between sn and ni . because pieces of unreacted ni - sheet were found in some of the annealed samples all further samples were kept at 1180  c for one week with repeated shaking of the quartz tube for homogenization . in addition , the samples were powdered , pressed into pellets and melted in vacuum again to ensure homogeneity . after alloying , the samples were annealed at 700  c for at least two weeks and subsequently quenched in water . the samples were then cut or broken into three pieces for investigation by xrd , sem and differential thermal analysis ( dta).1 powder xrd data for phase identification of most samples were recorded on a bruker d8 powder diffractometer equipped with a high speed lynxeye one dimensional silicon strip detector and an x - ray cu tube . a smaller number of samples were investigated in a huber guinier image plate camera ( huber gmbh , rimsting , germany ) on a siemens kristalloflex erl 1000 generator ( siemens ag , berlin , germany ) with cu k1 radiation . in both cases the patterns were analysed using the crystal structure data for phase identification were taken from pearson 's handbook of intermetallic phases . samples to be examined by optical light microscopy and sem were embedded in a phenolic resin mixed with carbon ( struers , denmark ) by hot - pressing . ( in , sn)-rich samples that were partially liquid at the annealing temperature were embedded in a cold mounting resin in order to avoid melting of the low - melting phases during embedding . then the samples were ground with sic discs with 1201200 mesh and polished with al2o3 ( 1  m ) to obtain a smooth surface . samples embedded in the cold - mounting resin had to be contacted before the sem measurements because this resin is non - conductive . metallographic investigations were performed using a light microscope ( zeiss axiotech , jena , germany ) . a dsc - s75 digital still camera ( sony , tokyo , japan ) switched to full zoom was employed to take pictures . sem including epma ( electron probe micro analysis ) measurements were carried out on a cameca sx 100 instrument ( cameca , paris , france ) electron probe using wavelength dispersive spectroscopy ( wds ) for quantitative analyses and employing pure ni , in and sn as standard materials . the measurements were carried out at 20  kv with a beam current of 20  na . conventional zaf matrix correction was used to calculate the compositions from the measured x - ray intensities . a number of samples were investigated on a scanning electron microscope jeol jsm-6460 using an edx analyser . this instrument was calibrated using pure ni and sn as well as inas . as the combination of in and sn is not favourable for edx investigations due to the overlap of the respective l lines , several of these samples it turned out that , despite this overlap , the edx results were reliable . for each individual measurement the not normalized sum of mass per cent was checked . only measurements with values between 97 and 103  wt.% . were taken because large deviations from 100 would indicate e.g. the presence of additional elements in the sample ( e.g. impurities ) or the beam spot being located on a hole that lead to erroneous results . the full assessment will be published elsewhere   and therefore only brief information about it will be presented here . the above mentioned theoretical assessments of in  ni , in  sn ( based on ) and ni sn   were used as the base for the calculation of phase equilibria in the ternary in the experimentally observed ternary phase was modelled using the crystallographic information about the c2mou prototype . two of them are fully occupied by ni atoms , the other two are partially occupied by in and sn in the same manner . therefore these positions were joined into the two - sublattice model allowing a solubility between in and sn in the form ( ni)1(in , sn)1 . because of the experimentally measured solubilities of third elements in all intermetallic phases and the existence of complete mutual solubilities , the models used in the binary assessments were expanded and/or unified to accommodate them . in the asni structure type family the structures hp4 ( asni ) and  hp6 ( inni2 ) represent the limits in the degree of filling of the 2d  position ( empty in asni , fully occupied in inni2 ) , but are otherwise identical . in order to allow for the modelling of continuous solid  solutions between such phases and in consistency with  crystallography they have to be described using the same model . in   the ni3sn2 ht - phase ( partially filled hp6 ) was described as  ( ni , va)1(ni , va)1(ni , sn)1 , which was expanded to ( ni , va)1(ni , va)1(in , ni , sn)1 in the ternary in similarly the description of the ni3sn lt and ni3 in phases was unified to ( in , ni , sn)0.75(in , ni , sn)0.25 because of the experimentally confirmed complete solubility between these phases requiring a reassessment of this phase in the in  ni system . the results obtained from these samples quenched from 700  c are shown in table  1 together with experimental information ( annealing time , edx or wds ) . areal edx scans were used to determine the composition of the matrix solidified from the liquid during quenching , which has been denoted by  solidified liquid  in table  1 . the experimental isothermal section based on these results is shown in fig .  1 . phase field boundaries are drawn using solid lines , and tie lines as derived from two - phase samples using dotted lines ; the liquidus is shown by a dashed line since its course is estimated from the limited number of areal edx measurements of the respective samples ' matrices . two ternary compounds have been reported in the literature , inni6sn5 and in2nisn . while inni6sn5 ( labelled t in fig . 1 ) was found as a true ternary compound in the present study ( in the sense that it is entirely separated from other compounds by two - and three phase fields ) , this was not the case for in2nisn . instead , the binary compound inni was found to dissolve considerable amounts of sn ( up to 28 at.% ) , and thus , at 700  c the assumed ternary phase is in fact part of the large ternary solubility of inni . this is also reflected by the course of the lattice parameters of inni ( fig . the homogeneity range of the ( ni ) solid solution was found to decrease from the sn- to the in - side in good agreement with the limiting binary values : 5.2  at.% sn in ( ni ) ( ) and 2.7  at.% in in ( ni ) ( sample in1 , in20ni80 ) . this latter value is smaller than the one reported in massalski 's version of the binary in  ni phase diagram   but is consistent with the values from ternary samples . 3 ) contains the two phases ( ni ) and ni3(in , sn ) from which the corresponding tie line could be established . for ni3(in , sn ) there is a continuous solid solution with a linear variation of the lattice parameter ( see fig . similarly , mutual solubility between inni2 and ni3sn2 ht has been proposed in the literature . indeed such a complete solid solution is likely since inni2 and ni3sn2 ht exhibit crystallographic structures hp4 ( asni - type ) and hp6 ( inni2-type ) , respectively . data obtained for the present study also suggest the existence of a complete mutual solubility between these two phases , since epma analysis of samples placed along this section did not reveal the presence of a two phase field between the two phases , and no corresponding three - phase fields were found in samples on either side of this section . the development of the lattice parameters from the ni3sn2 ht to the inni2 region are shown in fig . the lattice parameters from xrd were plotted vs. the respective in content of the ni3sn2 ht phase as determined by epma in two - phase samples ( samples ins16 to ins20 and in3 ; see table  1 ) . . 62.5  at.% , which is required for comparison , because the lattice parameters also change significantly as a function of the ni - content . it can be seen that there is no indication for the existence of a two - phase field in the course of the lattice parameters , either . this situation is therefore in good agreement with the evaluation of bhargava and schubert   who proposed a complete solid solution between inni2 and ni3sn2 ht . in massalski 's version of the binary in  ni phase diagram a considerable homogeneity range of approx . phase analysis in the ternary system , however , did not reveal any significant solubility range along the in  ni axis , i.e. the phase is almost stoichiometric with respect to the in  ni binary ( see the results listed in table  1 ) . however , there is an appreciable ternary solubility of sn with a limiting concentration of 5.4  at.% , which was derived from sample ins41 , in35ni58sn7 , comprising the three phases ni3sn2 ht  +  in9ni13  +  inni . ht . therefore , in contrast to the literature , binary in9ni13 is in fact a line compound having a ternary solubility of sn . this value is smaller than the value given in ref .  , which was derived from furnace - cooled samples . considering these results , the huge solubility of in in ni3sn4 reported by huang and chen   at 160 and 240  c appears rather unlikely and seems to be a non - equilibrium effect caused by the low annealing temperature . the determination of the compositions corresponding to the three - phase field [ ni3sn2 ht  +  ni3sn4  +  inni6sn5 ] by epma was complicated by the low compositional contrast ( samples ins1ins2b ) so that the data were derived from line scans . at 700  c no binary solid in any such phase found in the phase analysis is therefore a product of solidification of the liquid during quenching of the sample . based on the results from xrd and epma , three three - phase fields were identified in this region : [ l  +  ni3sn4  +  inni6sn5 ] , [ l  +  inni  +  inni6sn5 ] and [ l  +  in3ni2  +  inni ] . the determination of the composition of the liquid was done using areal scans on the solidified matrix found in the respective samples . 7 shows the micrograph of sample ins34 , in60ni30sn10 , quenched from 700  c where the phases in3ni2 and inni  solid at the annealing temperature  and the solidified matrix can be seen . 8 shows the micrograph of sample  ins32 , in40ni30sn30 , on which the three - phase field [ l  +  inni  +  inni6sn5 ] is based . the black spots in the matrix are holes , while there are also precipitates of additional phases . together with the decomposition of the liquid phase ( even at relatively high cooling rate ) this lead to a higher uncertainty of the composition values listed for the relevant samples in table  1 . however , it is clear that this situation needs to be further refined in conjunction with the low - temperature experiments currently being carried out . sn ternary system , based on the experimental data presented in this work , is shown in fig . the solubilities in the pure elements and in the liquid phase along the binary edges are defined by the employed binary assessment and agree reasonably well with the experiments . the continuous solubilities between ni3sn lt and inni3 as well as between ni3sn2 and inni2 , respectively , are correctly reproduced , and the obtained solubilities in binary compounds correspond to the experimental results , too . however , there is significant difference for the concentration of the liquid in the three phase fields [ l  +  ni3sn4  +  inni6sn5 ] and [ l  +  in3ni2  +  inni ] which may be caused by the uncertainties in the measurements of the liquid composition by areal edx scans . a complete isothermal section at 700  c was established in this  study for the in while it agrees well with previously known parts of the phase diagram it was enhanced with  new information , also including a slight revision of the homogeneity range of the binary in9ni13 phase , which was found to  be a line compound . calphad modelling was employed to provide  a calculated version of this isothermal section based on the  presented experimental results . the sublattice models for  the  ni3sn2 ht and inni2 ht phases were harmonized as ( ni , va)1(ni , va)1(in , ni , sn)1 to allow for the modelling of a complete solid solution between these two phases . however , a full assessment of this ternary system still lacks knowledge on the thermal behaviour as well as on reliable low - temperature phase equilibria . these are currently under investigation and will therefore form a separate publication   together with the details of the full thermodynamic assessment .
the phase equilibria of the ternary system in  ni  sn were investigated experimentally at 700  c using x - ray diffraction ( xrd ) and scanning electron microscopy ( sem ) including electron micro probe analysis ( empa ) and energy dispersive x - ray spectroscopy ( edx ) . 
 a corresponding isothermal section was established based on these results . 
 this particular temperature was chosen because it allowed obtaining reliable results within reasonable time . 
 the existence of the ternary phase inni6sn5 was confirmed whereas the ternary compound in2nisn , reported earlier in literature , was found to be part of a large solid solution field based on binary inni . 
 the ternary solubility of the binary phases was established , and continuous solid solutions were found between the isostructural phases ni3sn lt and inni3 as well as between ni3sn2 ht and inni2 . in addition , this isothermal section could be well reproduced by calphad modelling . the resulting calculated isotherm at 700  c is presented , too , and compared with the experimental results .