Characterization

of gold-palladium-silver

palladium-silver

for ceramic-metal

and restorations

Eugene F. Huget, D.D.S., MS.,* Nitin Dvivedi, Howard E. Cosner, Jr.*** United States Army Institute of Dental Research, Washington, D. C.

M.E.IMech.),** Division

of

and Dental

Materials,

L

ight-colored precious-metal casting alloys have been available for several years. High-fusion temperature ranges, relatively poor casting characteristics, and questionable tarnish resistance have contraindicated the routine use of these materials in ceramic-metal restorations. Recently, however, the so-called white golds have gained increased attention as potential substitutes for the more costly yellow alloys. Several white alloys intended primarily for use in ceramic-metal restorations have appeared on the commercial market. Sufficient data regarding the characteristics of these materials are not available in the dental literature. The present study was conducted to determine the mechanical properties of three commercially available high-fusing white ceramic-metal alloys? and to relate these properties to composition and microstructure. MATERIALS

AND

METHODS

Preparation of tensile specimens. Patterns for tensile specimenswere prepared by injecting molten wax into a split metal mold. The design and size of the specimens were as described in ADA Specification No. 14 for dental chromium-cobalt casting al1oy.l The geometry of the grip ends of the bars as well as sprueing arrangement are described in detail in the literature.2-4 The patterns were invested in a phosphate-. Commercial materials and equipment are identified in this report to adequately specify the experimental procedure. Such identification does not imply official recommendation or endorsement nor does it imply that the equipment and materials are necessarily the best available for the purpose. *Lieutenant

Colonel,

**Specialist

5th

***Certified

Dental

tCera.mco White, Hartford, Corm.; and

58

DC,

Class,

USA;

DC,

Technician, J. Aderer, Cameo-Lite,

USA;

Chief,

Division

Mechanical Division

of Dental Engineer,

of Dental

Materials. Division

of Dental

Materials.

Materials.

Inc., New York, N. Y.; SMG-W, J. F. Jelenko & Company, Inc.,

The J. M. Ney New Rochelle,

Company, N. Y.

gilur~; ”

3;

Characterization

for

ceramic-metal

restorations

59

bound refractory material. * The resultant molds were burned out at 1,500’ F. and then positioned in the cradle of the casting machine? so that the bar and sprue parts of the cavities were horizontally oriented. Casting temperatures of 2,650’ F. for Ceramco White and SMG-W and 2,500° F. for Cameo-Lite were used. The cast molds were bench-cooled to room temperature before retrieval and further handling of the test pieces. Preparation of specimens for microstructural evaluation and hardness testing. Discs measuring approximately 14 by 0.5 mm. were cast from each alloy by the same techniques as used for the tensile specimens. The discs were mounted in plastic and ground with abrasive papers of 240 to 600 grit sizes to remove gross surface defects. Final surface conditioning was accomplished with 0.05 ,prn alumina and a mechanical po1isher.f Metallographic specimens were etched by use of the following reagents and techniques: ( 1) immersion in a solution of 92 per cent HCl,§ 5 per cent H$O,,§ and 3 per cent HNO,§ by volume; (2) immersion in an aqueous solution of 10 per cent KCN and 10 per cent NH&O,; and (3) swab application of or immersion in HNO,.$ Unetched mounted discs were used for measurement of hardness. After determination of as-cast microstructure and hardness, the discs were removed from their mounts, heat-treated, remounted, and conditioned for further testing. Determination of mechanical properties. Tensile properties were determined on a constant-strain testing machine11 a t a crosshead speed of 0.02 inch per minute. Elongation was measured over a 1 inch gauge length with a breakaway extensometer.1 The reported tensile properties are based on a minimum of six observations for each of the test materials. Brine11 hardness numbers (BHN) of the materials were determined by application of a 12.6 Kg. load# to the finished surfaces of cast specimens with a steel ball indenter of 1/Is inch diameter. Reported hardness values are averages of six measurements on each of duplicate (two) specimens. Determination of response to heat treatment. Softening temperatures of the alloys were determined by the following procedure. Cast discs were heated at successive 100’ F. increments from 400 to 2,OOOO F. The discs were kept at each treatment temperature for 5 minutes and then water-quenched. Hardness (BHN) was measured after each treatment. Hardening temperature ranges were then determined by monitoring changes in hardness (BHN) of annealed castings upon reheat treatment over the 400 to 2,000’ F. temperature range. To determine the effect of heat-treatment time on the restoration of hardness, specimens of Ceramco White and SMG-W quenched from 1,800’ F. and discs of Cameo-Lite quenched from 1,900° F. were subjected to six repetitive 5 minute heat “Ceramigold

investment,

Whip-Mix

+Electromatic induction casting $IScomet polisher, Buehler Ltd.,

Corp., machine, Evanston,

Louisville, Howmet Ill.

Ky. Corp.,

New

York,

N. Y.

BConcentrated. IjInstron

Universal

IStrain

gauge

#Kentrall

testing extensometer,

hardness

tester,

machine,

Instron

model model

MC-l,

Engineering

LG-51-12, Riehle

Corp.,

Canton,

Instron

Engineering

Testing

Machines,

Mass. Corp.,

East Moline,

Canton, Ill.

Mass.

60

Huget,

Dvivedi,

J. Prosthet. Dent. July, 1976

and Comer

CERAMCO -+

WHITE

CAMEO-LITE

TEMPERATURE,

Fig.

1. Effect

of heat-treatment

temperature

on hardness

of high-fusing

OF

white

alloys.

Initial heat treatment Smin. 1800 OF and water quenched.

treolment

Fig. 2. Effect alloys.

of reheat-treatment

TEMPERATURE

temperature

on hardness

of two

OF

gold-palladium-silver-based

treatments at 1,300° F. Each reheat treatment was terminated by water-quenching. Hardness (BHN) was measured after each reheat treatment. Heat treatment of tensile and hardness specimens was also accomplished by a simulated porcelain firing* cycle. Tensile properties and hardness (BHN) were de*(I) Degassing: Cast specimens were reheated from 1,200 to 1,950” F., held at 1,950” F. for 5 minutes, removed from the furnace, and cooled in open air. (2) Simulated application of opaque porcekzin: Specimens were heated from 1,200 to 1,825” F., removed from the furnace immediately on reaching 1,825” F., and cooled to room temperature in open air. (3) Simulated application of body porcelain: Specimens were heated to two successive firings from 1,200 to 1,775” F. Specimens were cooled to room temperature in open air after each firing. (4) Simulated application of glaze: Specimens were heated from 1,200 to 1,800” F., removed from the furnace immediately on reaching 1,800” F., and cooled to room temperature in open air.

~hlm&

"

“:j

Characterization

for

ceramic-metal

restorations

61

CAMEO-LITE

Initial heat treatment Smin. 1900 “F and water quenched.

TEMPERATURE,‘F

treatment

Fig. 3. Effect of reheat-treatment

2

temperature

-+.CERAMCO

on hardness of a palladium-silver-based

alloy.

WHITE

x

Fig. 4. Effect of reheat-treatment and

SMG-W

were

quenched

from

time on hardness of high-fusing white alloys. Ceramco 1,800” F. Cameo-Lite spetimens were softened initially

water-quenching from 1,900” F. All castings were water-quenched of six consecutive 5 minute reheat treatments.

White by

from 1,300” F. after each

termined on completion of the firing sequence. Hardness specimens were then returned to a 1,300° F. furnace, heated 20 minutes, and retested. To determine the effect of porcelain coating on hardness, a dental porcelain* was fused to one side of a series of discs cast from each alloy. Hardness (BHN) was measured on completion of the fusion procedure and again after an additional 20 minute treatment at 1,300° F. Chemical analysis and evaluation of microstructure. The constituents of the “as-received” materials were determined by wet gravimetric procedures. The surfaces of etched specimens were observed with an optical microscopet at *Ceramco porcelain, Ceramco, Inc., New York, N. Y. tunitron, model BN-11, Unitron Instrument Company, Newton Highlands,

Mass.

62

Huget,

Dvivedi,

and

Fig. 5. As-cast microstructures:

Table

I. Tensile

properties

Ceramco White,

(A)

of three high-fusing Ceramco

Property

(B)

white

White

W Heattreated* 96 f 72f 52i

84 -f 5t 575 3 46 k 3

17f 3

17 f 2

17,. 1

9f2

Cameo-Lite.

Cameo-Lite

As-cast

93 * 4t 71 f 5 5Ok 8

4

and (C)

alloys

87 f 4t 60 f 6 48 f 9

lOIt

SMG-W,

SMG-

Heaitreated*

As-cast

Tensile strength (X 10spsi.) Yield strength$ (X IO* psi.) Elastic limit (X 10sp:s.i.) Modulus of elasticity (X IO8p.s.i.) Elongation (per cent)

.I. Prosthct. Dent. July, 1976

Comer

6zt2

As-cast

Healtreated*

3t 7

83 + 67 63 f 2

10 181k 2

41 f 8

80 f 6t 60 31 3 48 i 4

17 * 3

15* I

5~t2

7Lt3

by the Heyn

(intercept)

7+z

2

*Simulated porcelain firing cycle. tStandard deviation. $0.2 per cent offset. a magnification method.5

of 400x. Average

grain

size was estimated

RESULTS Tensile properties of the alloys are summarized similar as-cast tensile properties. Heat treatment not elicit a significant change in tensile properties.

in Table I. The alloys exhibited by the porcelain firing cycle did

Volume

30

Xurnbrr

1

Fig. (B)

6. Microstructures SMG-W, and (C)

Characterization

following Cameo-Lite.

heat

treatment

for ceramic-metal

by porcelain

firing

cycle:

restorations

(A) Ceramco

63

White,

Alterations in hardness of the alloys induced by heat treatment are shown in Figs. 1 to 4. Softening of as-cast Ceramco White and SMG-W appeared to be complete after treatment at 1,800” F., whereas maximum softening of Cameo-Lite was attained by heat treatment at 1,900’ F. (Fig. 1). Rehardening of annealed specimens of Ceramco White, SMG-W (Fig. 2)) and Cameo-Lite (Fig. 3) occurred on reheat treatment at temperatures betwen 900 and 1,400’ F. Rehardening of the three alloys appeared to be complete at 1,300° F. Ceramco White, SMG-W, and Cameo-Lite gave maximum hardness (BHN) values of 175, 205, and 180, respectively, following a 20 minute hardening treatment at 1,300’ F. (Fig. 4). Continued treatment at 1,300’ F. did not produce a significant change in hardness. Heat treatment by the porcelain cycle increased the hardness of SMG-W by about 15 per cent but decreased the hardness of Cameo-Lite by about 12 per cent (Table II). Hardness of Ceramco White discs subjected to the cycle was not altered significantly. An additional 20 minute heat treatment at 1,300° F. increased the hardness .of specimens previously subjected to the porcelain firing cycle. Porcelaincoated and noncoated specimens of each alloy gave comparable hardness (BHN) values. As-cast microstructures of the alloys are shown in Fig. 5. Grain boundaries of as-cast Ceramco White and SMG-W were obscured by precipitates. As-cast specimens of Cameo-Lite were attacked vigorously by the etchants employed, and interpretable metallographic information was not obtained. Crystallographic features of specimens

64 Table

Huget,

Dvivedi,

II. Response

and

J. l’rosthet. Dent. July, 1976

Comer

of three high-fusing

white

alloys to heat treatment

Heat-treated by porcelain cycle* As-cast

Noncoated

Ceramccl White 150 f 5t SMG-W 169 f 4 Cameo-l,ite 184f 4 *Specimens cooled in open air. tstandard deviation.

Table

Ill. Compositions

Element

Gold Palladium Silver Tin Iridium

1

157 & 5t 195 f 5 162 zt 3

Ceramco

White

50.09 30.28 14.73 2.26 2.34

Coated

white

I

cycle plus at 1.300” F.*

Noncoated

144*4t 192f 3 167 f 4

of three high-fusing

r-

Porcelain

20 min.

167 f 37 215 f 5 194f 3

1

Coated

169 f 2t 210 f 6 189 f 4

alloys

SMG-

W

49.06 31.61 14.98 4.14 -

I

Cameo-Lite

0.95 49.95 42.20 6.66 -

subjected to the simulated porcelain firing cycle, however, were markedly improved (Fig. ti). Ceramco White exhibited the smallest grains (~17 ,prn) and SMG-W the largest grains (-21 pm). Grain size of Cameo-Lite averaged about 18 pm. Compositions of the alloys are given in Table III. Analysis showed that Ceramco White and SMG-W were ternary alloys of gold (~50 per cent), palladium (-31 per cent), and silver (-15 per cent), whereas Cameo-Lite was based on a binary system of palladium (+50 per cent) and silver (-42 per cent). All three alloys contained tin. An additional constituent, indium (~2 per cent), was found in Ceramco White. DISCUSSION Although Ceramco White, SMG-W, and Cameo-Lite exhibit significant compositional and as-cast microstructural differences, their tensile properties and responses to heat treatment are strikingly similar. Strength characteristics of the three alloys are comparable to those of hardened type III casting golds. These materials, however, are harder and less ductile than the type III golds. Gold-palladium-silver ternary alloys as well as palladium-silver binary alloys form a continuous series of solid solutions. Such alloys are not susceptible to precipitation or age hardening. However, data obtained on hardness measurement indicate that the alloys considered in this study can be age hardened. It would appear that base metal constituents play a significant role in the development and control of the properties of these materials. Ability of the test alloys to harden is attributed to the formation of indium- and tin-containing intermetallic compounds.

Volwm: 36 Numbw 1

Characterization for ceramic-metal restorations 65

SUMMARY

Properties, compositions, microstructures, and heat-treatment characteristics of three high-fusing white ceramic-metal alloys were studied. The materials displayed different compositions and as-castmicrostructures, but similar tensile properties and heat-treatment responses.Hardness of cast specimenssubjected to the porcelain firing cycle was increased by an additional 20 minute heat treatment at 1,300° F. References 1. American Dental Association: Guide to Dental Materials and Devices, ed. 6, Chicago, 1972, American Dental Association, pp. 207-209. 2. Civjan, S., Huget, E. F., Erhard, W. L., and Vaccaro, G. J.: Properties of Surgical Casting Alloys, J. PROSTHET. DENT. 28: 77-81, 1972. 3. Civjan, S., Hug-et, E. F., Godfrey, G. D., Lichtenburger, H., and Frank, W. A.: Effects of Heat Treatment on Mechanical Properties of Two Nickel-Chromium-Based Casting Alloys, J. Dent. Res. 51: 1537-1545, 1972. 4. Civjan, S., Huget, E. F., and Marsden, J. E.: Characteristics of Two Gold Alloys Used in Fabrication of Porcelain-Fused-To-Metal Restorations, J. Am. Dent. Assoc. 85: 1309- 13 15, 1972. 5. American Society for Testing and Materials: ASTM Standards, Part 31, Philadelphia, 1964, American Society for Testing and Materials, p. 234. UNITED STATES ARMY INSTITUTE OF DENTAL WALTER REED ARMY MEDICAL CENTER WASHINGTON, D. C. 20012

RESEARCH