The Age Hardening of Silver with Copper-Silicide

Transcription

1 Mntana Tech Library Digital Mntana Tech Bachelrs Theses and Reprts, Student Schlarship The Age Hardening f Silver with Cpper-Silicide Jseph Edward Shaw Fllw this and additinal wrks at: Part f the Ceramic Materials Cmmns, Envirnmental Engineering Cmmns, Gelgy Cmmns, Gephysics and Seismlgy Cmmns, Metallurgy Cmmns, Other Engineering Cmmns, and the Other Materials Science and Engineering Cmmns Recmmended Citatin Shaw, Jseph Edward, "The Age Hardening f Silver with Cpper-Silicide" (1939). Bachelrs Theses and Reprts, This Bachelrs Thesis is brught t yu fr free and pen access by the Student Schlarship at Digital Mntana Tech. It has been accepted fr inclusin in Bachelrs Theses and Reprts, by an authrized administratr f Digital Mntana Tech. Fr mre infrmatin, please cntact sjuskiewicz@mtech.edu.

2 THE.;,GE HARDENING OF S liner with COT.'PER-SILlCIDE By Jseyh Edward 3havv Butte, Mntana,d. Thesis Submitted t the Department f!j1etallurgy in Partial Fulfillment f the equirements fr the Degree f Bachelr f 3cience in Iv.etallurgical Engineering 1..0NT.L1.T.h. SCHOOL 0]'MINES BUTTE, MONTAN.a. M.l..Y5, 1939

3 TABLE OF CONTEN'rS Heading Page Intrductin Thery f Age Hardening Experimental Hardness.. '.Vrk Results..., Cnc;lusins Suggestins fr Future Wrk 12

4 THE AGE HARDENING OF SILVER with COPPER-SILICIDE By Jseph EdWard Shaw Butte, Mnt ana A Thesis Submitted t the Department f Metallurgy in Partial Fulfillment f the Requirements fr the Degree f Bachelr f Science in Metallurgical Engineering MONTANA SCHOOL OF MINES BUTTEr MONTANA MAY 5, 193~ ::7975

5 s- THE AGE HARDENING OF SILVER WITH COPPER-SILICIDE Intrductin The successful applicatin f the phenmenn f precipitatin hardening t aluminum and cpper has indicated the pssibility f hardening all metals in the same way. The phenmenn f age hardening was discvered by Wilm l ) in 1911, and since that time much research has been carried n in all parts f the wrld n varius ally systerns. Due t the fact that sterling silver and silver plate are easily scratched r dented, it is evident that sme such hardening f silver is desirable. Silver has been hardened by a number f hardening elements, amng which are: cpper and aluminwitl, cadmium, cpper and cadmium, palladium and cpper, Silicn, cpper and Silicn, zinc, cpper and Zinc, cpper and magnesium, cpper and antimny, magnesium and Zinc, and cadmium and antimny.2) In this wrk cpper-silicide, CU 3 Si, was used as the hardening cnstituent. In "The Cnstitutin f the Cpper-silicn System,tI Smith 3 ) did nt find this cmpund t exist in the free state, hwever, the tw allying elements were used in a rati t prduce a phase, CU Si. 3 1) A. Wilm Metallurgie 8, 225, (1911) 2) Lc. Cit. 3) C. S. Smith, "The Cnstitutin f the Cpper-Silicn System." Tr. A.I.M.E., Inst. Metals Div., 439 (1929) -1-

6 Thery f Age Hardening The thery f age hardening was prpsed by Mercia,4) Waltenberg and sctt. 5 ) The cnditins necessary fr age hardening seem t be the frmatin f a slid slutin with a variable alpha range, in which the slute becmes mre sluble at higher temperatures. In such an ally, which may be a true binary r a pseud-binary system, the slid slutin is heated in the hmgeneus alpha field and then quenched, leaving a super-saturated slutin which retains its hmgeneity at rm temperature. Annealing at sme temperature belw the slubility curve causes the slute t be thrwn ut f slutin in fine submicrscpic particles dispersed alng the planes f slip. These particles, either by slip interference 6 ) r lattice distrtin, prduce the hardening effect. 4) Mercia, "The Age Hardening f Metals." Tr. A.I.M.E. 99, 13 (1932) 5) Mercia, Waltenterg, Sctt, U. S. Bur. f Stds. Sci. Paper 347 (1919) 6) Jeffries and Archer, "The Slip Interference Thery f Hardening." Chem. and Met. Eng., 24 (1921) -2-

7 Experimental Wrk The allys were prepared frm pure silver, electrlytic cpper and silicn. All melts were made in a carbn resistr electric furnace, and all annealing was dne in an electric tube furnace, the temperature f which was cntrlled by a rhestat. Graphite crucibles were used fr all melts. Fusin temperatures were measured with an ptical pyrmeter, and annealing temperatures were measured with a platinum thermmeter. Cpper-silicide was first made by melting tgether cpper and silicn in the crrect prprtins t frm the cmpund, CU 3 Si. (12.85% 8i and 87.15% Cu) Several pieces f charcal were placed n the charge t prevent it frm xidatin. After a prper length f time sufficient t insure hmgenity, the charge was remved frm the furnace and allwed t cl. A weighed prtin f the melt was then analyzed fr CU 3 8i. The silver allys were then prepared by melting tgether silver and cpper-silicide. After slidifying, the ally buttns were annealed fr ne hur at 800 C. and quenched t d away with the effect f fractinal slidifiatin. The specimens were hammered and rlled int strips with hand rlls, the strips being cut int small pieces fr individual treatment. -3-

8 Hardness The small individual strips were again annealed at 800 C. fr ne hur and quenched. This prcedure remved the effects f cld wrk and assured a super-saturated slid slutin at rm temperature C. was fund t give mre cnsistent results s was used as the temperature frm which t quench in all f this wrk. Nw, heating the ally t sme temperature belw the slubility curve caused precipitatin f the slute, thereby prducing the hardening effect. Fr each temperature selected the hardness f the specimen was tested at regu- Lar intervals. Hardness measurements were made n a Rckwell superficial hardness tester, using a 15 kilgram lad and a ne-sixteenth inch ball. Due t the fact that precipitatin and agglmeratin f particles d nt take place at the same rate f velcity, the hardness measurements vary ver a range f three r fur pints. This variatin gradually dereases until cmplete precipitatin is had, after which the sftening is cnsistent. Upn annealing the ally at C. it was fund that the maximum hardness btained was belw that btained at lwer temperatures. The cause f this is that the rate f '-4-

9 agglmeratin f the particles is much faster than the rate f precipitatin, and the size f the particles becmes t large in a very shrt time t give a maximum hardness. On annealing at higher temperatures the maximum hardness was btained in ne r tw minutes, while at lwer temperatures the maximum hardness was nt btained s sn. The lngest time required t btain the maximum hardness was abut twenty minutes, and the hardness persisted ver lnger perids f time when aged at these lwer temperatures. The maximum hardness btained fr any specimen was n the 2.5% Cu 3 Si ally upn aging fr twenty minutes at C. This hardness was abut 43 n the scale used. The rate f hardening was fund t be related t the temperature, that is, the higher the temperature the less time needed t get the maximum hardness. If the temperature was t high, hwever, the maximum hardness was nt btained. This ally system seems t be an exceptin t the general rule. In mst f the systems that exhibit the phenmenn f age hardening, the maximum hardness btainable increases with the amunt f hardening agent used up t a certain pint, being different fr each system. The maximum -5-

10 hardness ttained fr each ally investigated was very nearly the same, teing between 38 and 42 n the scale used. Althugh the hardness des nt increase, the allys becme mre trittle and much harder t wrk as the amunt f hardening agent is increased. Upn annealing the specimens in air they became xidized and disintegrated, and rlling was fund t be very difficult. A reducing atmsphere was fund t prevent these difficulties, hwever, this was discvered t late t be used in this wrk. -6-

11 TABLE I-Change In Hardness with time at Varius Temperatures Ally N.1 (95% Ag, 5% CU 3 Si) Reheating Temp. Degree s C. Reheating Time in Minutes Rckwell Hardness 15 kg. Lad As Quenched As Quenched As Quenched As Quenched

12 0 '<;ff ('J) Q) ~ ::J q 0.,-( t<) ~ c:.,-( 0 CIJ Q) a.,-( E-t t CIJ rl CIJ U"J: 91/1-8: -8-

13 TABLE II-Change in Hardness with Time at Varius Temperatures Reheating Temp. Degrees C. Reheating Time in Minutes Rckwell Hardness 15 kg. Lad As Quenched ? ? As r-iuenched As Quenched ? ? As Q.uenched ? Of r:anes J..lBRAR~ N10NTAl~A SCHOOL BUI'IR -9-

14 0 )( III rl CJJ t<) ::J 0 0 i 'G~ rl/w C\l 4- t ~ - \ j ~~ V t<) r----_ ~ C\l r-i QD <tl 0 '<;fl :>. 0 r-i r-i Ul <tl <D +' D ::J q C1 rl 0 rl +" t<) ~ ttl <D q.q rl <D p:j (1) El c: rl Ul C\l r (1) q c ~ttl tn C1 0 rl r-i <D QD q i C\l 0 0 m..c: 0 SS8UP.IBH 118M){OOH

15 Cnclusins Silver can be age hardened by the additin f cpper-silicide. The hardness increases rapidly at annealing temperatures between C. and C. The maximum hardness was btained after aging fr twenty min utes at a temperature f 200 C. Cntinued aging at this temperature caused a decrease in the hardness f the ally due t agglmeratin f the hardening cnstituent. An increase in the cpper-silicide cntent abve 2.5% fails t give an increase in the hardness f the ally -11-

16 Suggestins fr Future ~rk The determinatin f the psitin f the slubility curve wuld aid greatly the future wrk n this ally. A reducing atmsphere seems t be necessary fr all annealing and aging t prevent disintegratin and xidatin f the specimens. As the maximum hardness was btained at the lwest temperature tried, it seems lgical that even lwer temperatures shuld be tried. An ally cntaining a lwer percentage f cpper-silicide may even be desirable. -12-

17 I wish t acknwledge the help and guidance f Dr. Curtis L. Wilsn, head f the Metallurgy Department at the Mntana Schl f Mines, under whse supervisin this wrk was perfrmed, and wh als aided with the writing f this thesis. -13-