Heat treatable platinum experi¬ences a significant increase in strength and hardness because of microstructural transformations brought about by thermal processing during manufacturing procedures. Conventional platinum alloys derive their
increased strength and hard¬ness solely from work hardening during cold forming. Platinum alloys generally classified as heat treatable are based on varying additions of tungsten (W), gold (Au), gallium (Ga), indium (In), palladium (Pd) or
copper (Cu) according to industry sources.
Information on these alloys was derived from studies in the late 1970's, published in 1990. Certain patents on their applica¬tion were obtained in the mid 90's. This class of materials was
marketed and sold in Europe in the late 1980's. Based on international hall¬marking standards requiring a mini¬mum of 95% content for unqualified designation as platinum jewelry, the simultaneous control of chemistry and thermal processing
affords a means of manipulating physical properties over a broad range. The inherent low hardness and wear resistance of certain platinum alloys can be overcome with heat treatable platinum. Recent publications have focused on properties
and processing issues with limited discussion of potential usage (1998, 1999).
Properties of heat treatable plat¬inum are compared to industry stan¬dard 95% Platinum 5% Ruthenium, 95% Platinum 5% Cobalt or 90% Platinum 10% Iridium
alloys.
MELTING TEMPERATURES & COLOR
Alloying additions required to impart response to heat treatment reduce the melting range of 95% Pt materials substantially (145°C). The melting range is broad at 100°C com¬pared
to the narrow 10-20°C typical of most platinum alloys. Care and attention to this unique melting range must be exercised when using brazing or self welding methods for assembly. Color characteristics indicate a quality platinum shade. The
lightness value (L*) matches well. The overall color difference vector value is very close match between the standard and heat treatable materials. The abbreviation HTA™, short for heat treatable alloy, is used throughout the
remainder of the document.
AS-CAST PHYSICAL PROPERTIES:
The cast hardness of heat treatable platinum is higher than conventional materials. Likewise, the strength of heat treatable platinum is considerably higher. This
means forces required to close settings are higher, but the result is more secure. Polishing times are significantly faster for the harder heat treatable material. Scratch and wear resistance are also much improved from the elevated
hardness.
WROUGHT PHYSICAL PROPERTIES:
Heat treatable platinum has a significantly different response to cold working compared to conventional materials.
In general, strengths of heat treatable platinum greatly exceed what can be obtained in conventional materials. This is especially true with the yield strength where an elevated value is critical for spring like properties. These enhanced properties can be obtained through cold working, heat treatment alone or a combination of both.
Heat treatable platinum hardness is higher than heavily cold worked 95Pt5Ru. Heat treated strength exceeds the possibilities achieved through cold working conventional materials. All of this additional strength and hardness is
achieved without sacrificing ductility for forming operations.
Heat treatable platinum requires more energy to deform than conventional materials. This implies it absorbs more energy before deforming plastically, thus exhibiting
superior spring properties. Spring hard material subjected to an aging heat treatment exhibit a high level of strength with almost 15% elongation or ductility. This is similar to a spring steel. Likewise, the aged soft material has
ductility with strength. The soft material exhibits maximum ductility for forming operations.
Combinations of rolling and aging treatments can be applied to provide a wide range of properties to suit most forming operations. This
diver¬sity of strength and ductility simply cannot be achieved with convention¬al materials.
APPLICATIONS:
Investment Cast Articles:
Heat treatable platinum exhibits a lower melting point, superior strength
and a high hardness to enhance wear resistance while reduc¬ing polishing time. All of these attrib¬utes can contribute to unique design options for investment cast applica¬tions. Care must be taken to com¬pensate for the reduced melting
range during assembly brazing or welding operations. With double the hardness and yield strength, a high level of setting skill is required.
Hand Forged Wire Assemblies
Delicate, high strength designs can be hand forged from heat treat¬able platinum wire.
Findings and Hardware:
Heat treatable platinum has found increasing application in the area of jewelry findings where supe¬rior
spring properties are required for functionality.
Seamless Bands:
The unique machinability of heat treatable platinum provides numer¬ous applications for machined and engraved seamless bands.
Conventional platinum
alloys are tough on milling and engraving tool¬ing. Rapid chip hardening and self welding tendencies limit design options or cause excessive manufac¬turing time to be devoted to tooling changeovers or sharpening. With heat treatable
platinum, many of these difficulties are reduced. Tool life can be 5-10X longer. This is espe¬cially advantageous for CNC work where re-setting tooling amounts to expensive downtime. Diffusion bond¬ing can be performed under the same
conditions as conventional alloys.
The 1998 & 1999 presentations on heat treatable platinum outlined a number of manufacturing issues and potential applications for the material. Virtually all of the pro¬posed techniques and
products have become reality over the past three years. Properties manipulations through the combination of cold working and thermal processing pro¬vide a range of elevated strength and hardness that cannot be achieved with conventional
alloys such as 95Pt5Ru and 90Pt10Ir. Many of the obstacles in primary manufacturing processes that affected the size and weight of stamping coils have been surmounted by incorporating specif¬ic heat treatments into unique sched¬ules.
This means specially cast thin billets weighing 500 t.oz can be processed into strip coils in excess of 125 t.oz to assist high volume stamp¬ing demand. Likewise, tube billets of the same size contribute to 200 t.oz lots of finished
product for volume seamless band demand. Wire coils 250 t.oz in weight can be produced at a variety of sizes. Research efforts continue to develop techniques that improve the surface finish quality and properties uniformity for
repro¬ducible performance in demanding secondary manufacturing processes.
The application of heat treatments enhances the properties, wear resist¬ance and functional life of finished products. This enhancement can be achieved
through mass production atmosphere belt furnaces common to the jewelry trade or torch heating by hand on an assembly bench. The material responds to a broad variety of treatments to achieve increased hardness. Specialty over aging
treat¬ments to create a free machining microstructure or provide properties uniformity to stamping coils require specialized equipment and tech¬niques.
SUMMARY:
- Heat treatable platinum has a higher as-cast hardness than conventional materials. This enhances retention of a bright polished finish. Manufacturers have noted a 40% reduction in finishing times compared to 95Pt5Ru for the same
styles.
Work hardening occurs at a much faster rate with heat treatable platinum alloys. They can achieve a higher hardness and yield strength than conventional alloys with superior spring properties. Mass produced findings take advantage of these attributes.
Correct heat treatments increase hardness and yield strength about 60% above the soft state. Final properties are double the strength of conventional materials such as 95Pt5Ru or 90Pt10Ir. Hand forged designs capitalize on this behavior. - Abroad range of hardening treatments from torch heating fo lowed by air cooling to travel through an atmosphere belt furnace will cause a significant increase in physical properties.
- Performance during machining operations is substantially better with the free machining microstructure compared to conventional materials. Stone set and engraved seamless bands take advantage of these attributes of heat treatable platinum.
- Bi-metal seamless bands can be diffusion bonded just like conventional materials
- Superior engraving performance of heat treatable platinum enhances productivity for eternity band styles of rings.
V10N9
Practical Applications of Heat Treatable Platinum
Greg Normandeau
IMPERIAL SMELTING & REFINING CO. OF CANADA LTD.
This is an abbreviated version of the original work. For full technical details, please consult the original paper.
