conditions for shs of intermetallic compounds with selective laser

8/12/2019 Conditions for SHS of Intermetallic Compounds With Selective Laser

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Combustion Explosion and Shock Wave s Vol . 35 No. 2 1999

o n d i t io n s f o r S H S o f I n t e r m e t a l l ic o m p o u n d s w i t h S e le c t iv e L a s erS in te r i ng o f P o w d e r e d o m p o s i t i o n sI . V . S h i s h k o v s k i i 1 A . G . M a k a r e n k o 2 a n d A . L . P e t r o v I UDC 621.373.826:536.46

Translated from Fizika Goreniya i Vzryva Vol. 35, No. 2, pp. 59-64, Mach-April 1999.Original article submitted January 1, 1998; revision submitted July 15, 1998.The se lec t ive laser s in ter ing of powdered mi xtures t radi t ional ly used in h igh-temp era tur e synthes is technology is s tudied. I t is shown tha t a cont rol led exothermi ccombu stion reac tion can be set up in the focal spot o f a CW Nd-YAG laser. T he re-qui red laser in terac t ion parzmete rs (power , scan ra te , and laser beam diameter ) an ddispers i ty and composi t ion of the powder composi t ion are d e term ined for th is modeof prepar ing thre e d imensional s~mples of in termeta l l ic compounds by se lect ive lasersintering.

I N T R O D U C T I O NSelective laser sintering of powdered composi-tions is a widespread method for creating three di-mensional objects, mate rial copies of models of ma-chine parts, in the rapidly developing technology oflaser synthesis of three dimensional pieces. An over-all view of the model and cross sections of its layers,according to which the object will be synthesized-

grown layer-by-layer on a vertically moving plat-form, are first stored in the memory of a personalcomputer using standard graphics packages. Thecomputer then controls the entire engineering pro-cess. The existing production equipment for selectivelaser sintering is traditionally intended for wax, ny-lon, polycarbonate, and acryl butadiene styrene. Thethree dimensional copies created out of these mate-rials can only serve as models and are used, e.g., forprecise casting in melta ble molds, which greatly easethe work of designers and reduce the time requiredto bring new technologies into production. Here thecasting molds can only be used a limited numberof times. The problem of fabricating single copies ofcomplicated models in such areas of human activityas prosthesis and restoration is also pressing. Thus,an intense search is under way for promising powdermedia for selective laser sintering in the technology oflaser synthesis of three dimensional pieces and stud-1Samara Branch of the Lebedev Physics Institute,Russian Academy of Sciences, Samara 443011.2Samara State Technical University, Saznara 443010.

ies are being made of the physical processes whichtake place when laser light interacts with powderedmedia. It has already been found that metal pow-ders coated with a polymer, as well as powders ofbimetals or ceramic materials can be used for threedimensional prototype production [1-4].The choice of promising powder compositionsfor selective laser sintering is mainly based on thepossibility of realizing liquid phase sintering during

laser int eraction. In these cases the composition is amixture of two or more powders with substantiallydifferent melting points. During sintering, the easilymelted phase flows over the grains of the refractoryphase and, on crystallizing, serves as a binder whichimparts a durability to the laser processed sinteringregion. Three dimensional objects grown by layer-by-layer synthesis are semifinished products that re-quire further work (e.g., annealing in an oven, infil-tration of a filler, etc.). The need for initial prepara-tion of the powder and for monitoring the surround-ing atmosphere and the temperature of the pow-dered medium on the platform where the sinteringtakes place make selective laser sintering relativelylong and complicated. This reduces the advantagesof this method compared to other methods for lasersynthesis of three dimensiona l pieces (such as laserstereolithography). Thus, besides searching for newpossibilities for selective laser sintering of powderedsystems and expanding the functional prospects forthe synthesized pieces, it seems reasonable to pro-ceed to the use of new gradient composite materi-als, as well as to combinations of laser sintering with

166 0010-5082/99/3502-016622.00 (~ 1999 Kluwer Academic/PlenumPublishers


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Condi tion s for SHS of Intermet aUic Com pou nds wit h Selective Laser Sint erin g 167

TABLE 1Powders

Aluminu m (ASD3,4)Filler powder (PG-SR4)

Ti tanium (PTKh-6)

Propert ies of the Powdered ater ials Used [ 4 6 7 ]D, ~m p, g/ cm 3 ps, g/cm3 r Tin ~10--50 1.25 2.7 0.54 66050-160 4.7 ~8.8 0.47 ~120030-60 1.23 4.5 0.73 1668

Q .n k J/m ol e ~ K10.8 27 317.5 59 ]" 1/ 3 115.5 48 1

No te s. D is the fraction size, p is the bulk density, ps is the solid density, ~ -- 1 - p/p~ is the porosity, Trn is t hmelt ing temperature , Qrn is the latent hea t of fusion, ~ is the atomi c mass, and K is the stoichiome tric coefficient.In the last column the up ward arrow indicates tha t one mass p orti on of the filler powder was mix ed with threepor t ions of a luminum and a downward arrow, that three mass por t ions of the same powder were mixed wi th onepor t io n of t i tanium.

other processes. Thus, combining laser sintering withsoldering [3, 5] makes it possible to produce three di-mensional models out of bimetals in which the highadhesion of the solder melt to the metallic phase im-proves the mechanical properties of the piece.

In this paper, we study the possibility of us-ing powdered exothermic mixtures, which are tradi-tionally used in the technology of self-propagatinghigh- temperature synthesis (SHS), for selective lasersintering, in particular mixtures based on stoichio-metric and nearly stoichiometric Ni-Al and Ni-Tisystems. Here it must be shown that a controlledexothermic combustion reaction takes place preciselyin the laser focal spot as the beam is scanned over thesurface of the powdered composite, since the shapeof the synthesized model can be maintained only byhigh-resolution spatially selective sintering. The useof selective laser sintering for SHS processes makes itpossible, both to obtain more durable materi al copiesof complicated pieces, and to extend the functionalcharacteristics of these three dimensional objects bysynthesizing intermetallic compounds.

MATERIALS AND EQUIPMENTSelective laser sintering is performed with theaid of a scanning laser beam from a computer con-

trolled CW Nd-YAG laser. Two standard lenses withfocal lengths f = 149 and 336 mm are used with theKVANT-60 laser system (the focal spot diametersof the laser beam are d = 50 and 100/zm, respec-tively). The laser power was varied over P = 1-16W and was monitored with an IMO-2A system atthe powder surface. The laser beam was scanned bythe computer over any previously specified profile toreproduce, layer-by-layer, a three dimensional objectwithin fields of 50 x 50 mm and 100 x 100 mm (i.e.,1024 x 1024 pixels) using mechanical deflectors. Thescanning speed depends on the time to shift the beamfrom point to point and on the time the deflectors

TABLE 2T h e r m a l a n d P h y s i c a l P r o p e r t i e s o f t h e N i - A I S y s te m [ 6 8 ]

Phase T i, ~ E , kJ / mole Q, J /kgNi2AI3 -- -- 1.9 9106NiA1 637 4- 25 135 4- 27 9.7 910 s

Ni3A1 652 4- 16 115 4- 25 2.4 9106Melt(Ni-FA1) -- 48.24 1.3.106

dwell on a point. It could be varied by the deviceover wide limits.The powders listed in Table 1 were used toprepare the SHS mixtures [4, 6, 7]. The PG-SR4(GOST 9722-79) filler powder contains 2.8-3.8 B,0.6-1.0 C, 3.0-4.5 Si, 15-18 Cr, ~


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168 Shishkovskll , Makarenko~ and Pet rov

Fig. 1. Equilibrium diagram of the Ni-A1 system [9]: 7-, 6-,and e-phase refer to Ni2AI3, NiAI, and Ni3A1, respectively.

E X P E R I ME N T A L R E S U L T SA N D D I S C U S S I O N

The powders to be p rocessed were poured freelyinto a volume clearly gre ater than the sintering depthof a monolayer. The conditions for combined selec-tive laser sintering and controlled SHS processingin a single pass of the laser beam were studied asfunctions of the laser power, s pot diameter, scanningrate, and powder composit ion. A controlled regime istaken to mean execution of the SHS exothermic reac-tion precisely at the wo rking point the so-called dif-fusion SHS mode). The range of the sintering depthh of a single monolayer for minimal distort ion of thislayer was determined.

Figure 2 shows plots of the experimentally ob-served effect of the laser interaction on a powderedcomposite based on a stoichiometric Ni-Al system.For P < 7 W and scan spe eds v > 25 cm/s ec, the sin-tering depths are shallow. The sintered monolayersdisintegrate upon contac t. As the power is raised andthe scan speed is reduced, the monolayers becomethicker. For P .~ 8.4-8.8 W Fig. 2a) and v ~ 2.9-8.6cm/sec Fig. 2b), a contr olled exothermic combus-tion reaction is observed visually precisely at thelaser focal spot. Final ly, for P > 8.8 W and v -- 25cm/sec Fig. 2a) and P - - 8.8 W and v < 2.9 cm/s ecFig. 2b), the exothermic reaction leading to forma-

tion of the intermetallic compound enters a frontcombustion regime in which the reaction front prop-agates through the entire side, independently of thelocation of the laser spot. These regimes can be re-garded as critical for the case where, in accordancewith the theor y of SHS, diffusion synthesis of the in-termetallic compounds transforms to front combus-tion of the powder mixture. In Fig. 2, this is indi-

cated with a dashed curve, since beyond that the sin-tering depth can no longer be determined reliably. Itshould be noted that, according to Fig. 1, the follow-ing phases can be observed in the different stages ofheating and cooling [9]. During heating to a tempera-ture below Te = 640~ the 7-phase Ni2Al3 nucleatesand grows; with further heating, the 7- and 6-phasescoexist; at temperatu res 1132 < T < 1638~ the7-phase melts and only the 6-phase NiAl remains;and, only after the melting temperature of the NiA1intermetallide is at tai ned T3 = 1638~ the inter-metallide NiA1 first develops and t hen the e-phaseNi3A1 forms wi th subsequent cooling. Therefore, de-pending on the chosen laser parameters and the com-position of the powder mixture, the laser energy maybe sufficient, or not, to reach the corresponding tem~peratures and to obtain the phases inferred from theequilibrium phase diagram in a model synthesizedby the selective laser sintering meth od.

The experiments showed that when the scatterin the particle fractions was increased substantiallyfrom a set size of 30-5 0/z m to 30-150 /Jm in an Ni-

A1 mixture of composition 3 : 1), intermetallides arenot formed when the powders are processed by theKVANT-60 laser d ~ 50/~m) , since the SHS processwas not observed. On the other hand, the scatter inthe size fractions has less effect on the formation ofintermetallides when th e diameter of the laser spot isincreased. This effect was made more precise on an-other laser system. Thus, processing the same pow-der mix with a spo t d iameter d ~ 0.5 mm on anLTN-103 system indicated a coincidence of the se-lective laser sintering and SHS processes. Equivalentprocessing on the LTN-103 laser system was ensuredby setting the laser energy flux 4P/~rd 2) in the spotequal to that for the KVANT-60 laser system. Thesame effect owing to the size distribution was ob-served in the Ni-Ti system.

Ni-Al syst ems wit h compositions 1 : 1, 2 : 1, and4 : 1 were also studied. The experiments showed thata deviation fr om the Ni3A1 stoichiometry greatlynarrows the range for optimum processing, so thatin some cases the selective laser sintering and SHSprocesses cannot be combined, while in others, thelow durability of the monolayers causes their embrit-tlement.

For powder compositions in the Ni-Ti systemexothermic reacti on 2)), the selective laser sinter-

ing and SHS processes were observed to combine forv = 2.6 cm/sec a nd P = 7.2-8.8 W. However, thesintered monolayers were less durable than for theNi-A1 powder composition. Adding a powdered ma-terial with a lower melting temperature to the Ni-Ticomposite [PG-19M-01 bronze powder TU 48-4206-


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170 S h i s h k o v s k i i , M a k a r e n k o , a n d P e t r o v

C O N C L U S I O N1 . C o m b i n e d s e l e c t i v e l a s e r s i n t e r i n g a n d S H S

h a v e b e e n r e a li z e d f o r t h e f i r s t t i m e i n a si n g l e e n g i-n e e r i n g p r o c e s s u s i n g p o w d e r e d c o m p o s i t i o n s b a s e do n s t o ic h i o m e t r i c N i - A 1 a n d N i - T i s y s t e m s w i t h aC W N d - Y A G l a se r . T h r e e d i m e n s i o n a l sa m p l e s o fp i e ce s m a d e o f t h e c o m p o s i t e m a t e r i a l s h a v e b e e no b t a i n e d .

2 . T h e o p t i m u m l a s e r p a r a m e t e r s f o r m a i n t a i n -i n g a c o n t r o ll e d e x o t h e r m i c r e a c t i o n p r e c i s e l y a t t h el a s e r f o c a l s p o t h a v e b e e n d e t e r m i n e d .

3 . A c o m p a r i s o n o f t h e l a s e r i n t e r a c t i o n t i m ew i t h t h e t h e o r e t ic a l l y c a l c u l a t e d i n d u c t i o n p e r i o d f o rt h e e x p e r im e n t a l ly d e t e r m i n e d p a r a m e t e r s P , v , a n dd s h o w e d t h a t t h i s t i m e i s s u f f i c ie n t f o r s y n t h e s i s o ft h e i n t e r m e t a l l i c N i 3 A 1 p h a s e r i g h t a t t h e l a s e r f o c a ls p o t .

4 . G o o d s e l e c t i v i t y c a n b e a c h i e v e d b y c o m b i n -i n g t h e s e l e c t iv e l a s e r s i n t e r i n g a n d S I t S p r o c e s s e s .T h e 6 1 # m w i d th o f th e e x o t h e r m i c r e a c t i o n z o n e isc o m p a r a b l e t o th e d i a m e t e r o f th e l a s er f o c a l s p o ta n d t o t h e d i s p e r s it y o f t h e p o w d e r m i x t u r e .

R E F E R E N C E S1. D. L . BoureLl, H. L . Ma rcus , J . W . Baxlow, and J .J . Beaman , S e l ec t ive l a se r s i n te r i ng o f me t a l andce rami cs , Int . J . Powder Metal lur . 28, No. 4, 369-

381 (1992).

2 . H . H a f e r k a m p , F . A l v en s l e be n , a n d J . G e r k e n ,R a p i d m a n u f a c t u r i n g b y l a s er s i n t er i n g a n d l a s ercladding, Laser Optoelektronik No. 3 ( June ) , 64-691 9 9 5 ) .

3 . D . M . G u r e e v , A . L . P e t r o v , a n d I . V . S h i s h k o v s ki i ,S e l e c t iv e l a s e r s i n t e r i n g o f b i m e t a l l i c p o w d e r c o m -

p o s i t i o n s , F i z . K h i m . O b r a b . M a t e r . N o . 6 , 9 2 - 9 7(1997).4. I . V. Shishkovski i , N. L . Ku pr iya nov , and A . L .P e t rov , Con di t i ons fo r l a se r d r i ven l aye r -by- laye rse l ec t ive s in t e r i ng ove r t he p ro f il e o f me t a l -po l ymercompos i t e s , Fiz . Khim. Obrab. Mater . No. 3, 88-93(1995).5. W. L . Weiss and D. L . Bou rel l , Select ive laser sin-t e r i ng o f in t e rme t a l l i c s , Metallurg. Trans. A 2 4 A ,No. 3, 757-759 (1993).6. M. I . Shi lyaev, V. E . Borzykh, and A. R. Dorokhov,L ase r i gn i t i on o f powdered n i cke l - a l umi num sys -t ems , Fiz . Goreniya Vzryva 30, No. 2, 14-18(1994).7 . O . V . L apsh i n and V . E . Ovcharenko , M at h ema t -i ca l mode l f o r h i gh- t empera t u r e syn t hes i s o f n i cke la l umi n i de Ni aA1 dur i n g t he rm a l exp l os i on o f a pow-d e r e d m i x t u r e o f th e p u r e e l e m e n t s , Fiz. GoreniyaVzryva 32, No. 3, 68-76 (1996) .8. I . K . K ikoin (e d.) , Tables o[ Physical Quantities:Handbook [ in Russian] , Atomizdat , Moscow (1976) .9. G. V. Sam sonov and I . M. Vini t ski i , Re]factoryCompounds: Handbook [ in Russian] , Metal lurgiya,Moscow (1976).10. V. N. Vi lyunov, Theo ry o] the Ignit ion o[ CondensedSubstances [ in Russian] , Nauka, Novosibi rsk (1984) .

conditions for shs of intermetallic compounds with selective laser

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