Sealing 304L to lithia-alumina-silica (LAS) glass-ceramics

Abstract

The f o m t i c n of a crack-free seal between a 300 series stainless steel an3 a glass-cemnic hzs in the past been very difficult. 'IZle p r L q cause of this difficdty Therefore, the ccrresponding g l a s s d c &mild have a similarly high t o w i l e the formtion of stress-free seals. Both a t E-M;-Mound and a t M;&G Zlect;-cnic ccxipnents, lithia-alumina-silica (m) glass-cadcs have ncw been scccessfully developed and sealed to 304L stainless steel. These mck-free seals have keen routinely fabricated using t m techniques: by adjusting the p r e n t glass carrposition c r by a d j u s t b g t i l e sealhg/qstallazation (or sealkg,/devitrification) cycle tht is r m t i n e l y used in forming seals between LAS glass-ceramic d nickel-&& alloys.seals were determined to be hennetic, w i t h leak rates of < cc/sec of Srp helium.Additional data on rn values and alloy yield strengths will be given which s h w the feasibility of using these materials in the manufacture of various cumponents including Veeco helium mass spectmwter leak tester.was fourid to have a leak rate of coqnnents w e r e helium leak tested; twenty feedthroughs an3 eleven p t e c b i c actuators {see Figure I) All the c a p n e n t s passed the helium leak test.samples were fabricated frcm 304L stainless steel and the effect on their tensfie strength was detemined as a function of the time-tenprature sealing/crystallizatim cycle. cycle of Figure 2 A match w a s also found with the 'baselinel glass that had been sealed b the stainless w i t h the proprietary d i n g / c r y s t a l l i z a t i a n cycle. (7) w e r e found routinely to be crack-free and hexmetic. Figure 2). I n Inanel-718 the strength was found * a increase after the cycle because of formation of the precipitation-hardenbg phase, Ni3Nb.sealing,/crystallization cycle neans that c m p n e n t s m a d e with 304L have the potential of Thus, the fact that the stahless steel iS weakened during the not beas strong as e m p n e n t s made w i t h Inconel 718. Although the stainless cmpnerlts m y not be as strong, this work shows they can be routhely prccfuced, and t h e i r seals c m be made crack-free and hennetic.c m p n e n t s khick do not Thus, 304L would be better suited f o r very h.k& s l z .-->- .3. 4. 5.6 . .a.9. 10.Miamisburg to N e t a l S e a l k g @ l , &caber Resultant after proprietary sealing/crystallization cycle.

Sealing Glass‐Ceramics with Near Linear Thermal Strain, Part I: Process Development and Phase Identification

“…The nucleation‐crystallization sequence is dictated by the thermal profiles. An attempt of sealing 304L stainless steel to lithia‐alumina‐silica glass‐ceramic incorporated a sealing temperature over 1000°C at which the glass‐ceramic is completely devitrified. The nucleation occurs at a low temperature (650°C–675°C) followed by a crystallization of Cristobalite at a higher temperature (800°C–830°C) to form high expansion glass‐ceramics.…”

The role of additives in a complex lithium silicate glass-ceramic

“…It has been known for a long time that silicate glasses containing lithia are particularly useful for glass-to-steel seals. These glasses crystallize at an easily accessible temperature and give rise to a glass-ceramic consisting of lithium disilicate (Borom et aI 1975;McCollister and Reed 1983;Haws et al 1986;Loehman and Headley 1987;Cassidy and Moddeman 1989;Moddeman et al 1989). The presently used sealing glass compositions contain several additives such as alumina, phosphorous pentoxide and alkali oxides, and understanding of the role of such additives requires further investigation.…”

“…For example the structural role of P205 as nucleating agent and the mechanism of action of AI20 3 in smoothing out thermal strains during partial ceramization are still unclear. Special schedules of thermal treatment are also in vogue in the applications of lithia-based silicate glass-ceramics (Borom et al 1975;McCollister and Reed 1983;Headley and Loehman 1984;Haws et al 1986;Moddeman et al 1989), and it would be interesting to understand the critical role of such heat treatment schedules. We therefore feel that it is important to investigate in detail this industrial glass-ceramic in order to appreciate clearly the role of the additives and the importance of the thermal histories accorded to glassceramics in their applications.…”