Investment Casting Materials — Choose the Right Alloy Early

1. Shrnutí

Investiční obsazení (lost-wax casting) is prized for shape accuracy, thin sections and complex geometry.

The choice of alloy is the single most important design decision because it determines: which materials and melting/degassing practices the foundry must use; the shell chemistry and firing cycles;

feeding and shrinkage strategy; achievable mechanical properties and required post-casting heat treatments; inspection and acceptance tests; and ultimately part cost and lead time.

This article examines the principal families of alloys commonly cast by the investment process, compares their metallurgical behaviors and processing implications, and provides pragmatic selection guidance tied to typical applications.

2. Why material selection matters in investment casting

Material selection is the single most consequential engineering decision in Investiční obsazení. It determines not only the in-service performance of the finished part (pevnost, odolnost proti korozi, Stabilita vysoké teploty, biokompatibilita, hmotnost),

but also the entire upstream and downstream manufacturing chain: melting and pouring method, shell chemistry and firing, gating/riser strategy, defect modes to watch for, required heat treatments, inspekční metody, doba cyklu, scrap risk and total cost.

3. Material families used in investment casting

4. Casting Alloy Materials — Determining the Final Performance of Castings

When selecting an alloy for a casting you must consider a set of interdependent factors: požadované mechanické vlastnosti (pevnost, houževnatost, únava), operating environment (teplota, korozivní média),

geometrie (thin walls vs massive sections), Výroba (tekutost, freezing range, reaktivita), post-cast processing (tepelné zpracování, HIP), inspection needs and cost.

Ferrous alloy castings

1) Carbon-steel odlitky

What they are: low-alloy steels where carbon is the primary strengthening element (NAPŘ., AISI 1020–1045, ASTM A216 WCB, ekvivalenty).
Vlastnosti & výkon: Mírná síla, good toughness when normalized, excellent machinability and low cost. Density ~7.85 g/cm³.
Casting considerations: modest melting point (~1,420–1,540 °C), good fluidity for many geometries but susceptible to shrinkage porosity in heavy sections.
Shell and gating design must provide adequate feeding. Hydrogen and graphite formation can be concerns for some grades.
Následné zpracování: normalizace, uhasit & zmírnit (v závislosti na ročníku) to achieve desired hardness/strength.
Aplikace: Strukturální komponenty, pouzdra, general engineering castings where corrosion resistance is not critical.

2) Alloy-steel odlitky

What they are: steels alloyed with Cr, Mo, V, PROTI, atd., ke zlepšení síly, hardenability and elevated-temperature properties (NAPŘ., 4140, 4340 family analogs).
Vlastnosti & výkon: Vyšší pevnost v tahu, fatigue resistance and toughness than plain carbon steels; can be heat-treated to high strengths.
Casting considerations: higher sensitivity to segregation and hot-cracking as alloy content rises; careful gating and risering needed; some alloys require vacuum or deoxidized melts for soundness.
Následné zpracování: critical quench/temper cycles, control of distortion during heat treatment. May require stress relief and tempering to balance properties.
Aplikace: rychlostní stupně, hřídele, high-stressed structural parts, oil-field components.

3) Nerezová ocel odlitky

What they are: iron-based alloys with ≥10.5% Cr; families include austenitic (304/316/CF8/CF8M), Martensitic (410/420), Duplex (2205) a precipitační vytvrzování (17-4 Ph).

Vlastnosti & výkon: corrosion resistance ranges from general (austenitics) to high chloride resistance (duplex/superduplex);
mechanical properties vary widely — duplex offers high strength + Dobrá odolnost proti korozi; 17-4 PH offers high strength after aging.

Casting considerations: stainless melts form oxide/slag; control of melt chemistry, deoxidation and inclusion removal matters for surface finish and mechanical properties.
Solidification shrinkage and hot tear susceptibility differ across grades.
Následné zpracování: rozpouštěcí žíhání, quench and aging (for PH grades); duplex may require careful heat treatment to keep phase balance. Passivation and pickling often follow machining.
Aplikace: chemical plant components, ventily, námořní hardware, sanitary parts, Zpracování potravin, zdravotnické prostředky.

Non-ferrous alloy castings

4) Aluminum-alloy odlitky

What they are: Al-Si, Al-Cu and Al-Mg families (NAPŘ., A356, A357, ADC12, 6061-typ) for cast components.
Vlastnosti & výkon: nízká hustota (~ 2,7 g/cm³), good specific strength (after heat treat for some alloys), excellent corrosion resistance when alloyed properly; vynikající tepelná/elektrická vodivost.
Casting considerations: very good fluidity enables thin walls and fine detail, but hydrogen porosity, oxide films and hot tearing in certain conformations are key risks.
Shell firing temperatures and dewax schedules differ from ferrous work. Hydrogen control, melt cleanliness and proper gating are essential.
Následné zpracování: solution heat treatment and artificial aging (T6) pro sílu; sometimes HIP for critical aerospace parts.
Aplikace: Letecké pouzdra, automotive lightweight components, heat-dissipating parts.

5) Měď-base alloys (bronz, mosaz, hliníkový bronz)

What they are: S-Sn (bronz), Cu-Zn (mosaz), s (hliníkový bronz), S námi, a varianty.
Vlastnosti & výkon: Vynikající odolnost proti korozi (especially Cu-Ni/Al-bronze), good bearing properties and thermal/electrical conductivity. Density ~8.4–8.9 g/cm³.

Casting considerations: lower melting points than steels; high thermal conductivity affects solidification behavior (fast cooling).
Good fluidity makes fine detail feasible. Shrinkage and hot cracking risk depend on alloy composition.
Následné zpracování: annealing for ductility, machining is often difficult (otužování práce); surface finishing and dezincification concerns for brasses exposed to certain environments.
Aplikace: námořní hardware, komponenty čerpadla, ložiska, decorative and electrical parts.

6) Titan-alloy castings

What they are: principally Ti-6Al-4V and other Ti alloys offering high specific strength and biocompatibility.
Vlastnosti & výkon: excellent strength-to-weight, corrosion resistance and biocompatibility; nízká hustota (~4.4 g/cm³).

Casting considerations: highly reactive melt (kyslík, nitrogen pickup) — vacuum/argon melting and pour required to avoid embrittlement and inclusions.
Solidification shrinkage and oxide formation demand specialized shell materials and melting practices. Production costs and equipment requirements are high.
Následné zpracování: vacuum heat treatment, úleva od stresu, HIP common to close porosity for critical components. Surface finishing is important for fatigue-sensitive parts.
Aplikace: aerospace structural components, lékařské implantáty, high-performance sporting goods.

High-temperature alloy castings

7) Nickel-base superalloys

What they are: Ni-Cr-Co-Al-Ti based alloys (Inconel, René, Nimonic families) designed for strength and creep resistance at elevated temperatures (up to ~1,000 °C and beyond for some alloys).
Vlastnosti & výkon: excellent creep strength, oxidation and corrosion resistance at high temperature; density around 8.2–8.5 g/cm³.

Casting considerations: long solidification ranges promote segregation and shrinkage defects; vakuové indukční tavení, strict de-gassing and inclusion control are critical.
Directional solidification and single-crystal casting are specialized variants for turbine blades (different process chain).
Následné zpracování: complex solution and aging heat treatments to develop γ′ precipitates; HIP and machining are common. Certification for aerospace sectors requires tight NDT.
Aplikace: gas-turbine hot-section parts, Aerospace, výroba energie, high-temperature chemical processing.

8) Cobalt-base alloys

What they are: Co-Cr-Mo and related compositions used where wear and elevated-temperature strength are required (NAPŘ., stellite family).
Vlastnosti & výkon: good hot hardness, wear resistance and corrosion resistance. Often used where sliding wear at elevated temperature is present.
Casting considerations: high melting points and sensitivity to segregation; machining is challenging due to high hardness.
Následné zpracování: solution/aging (where applicable), grinding and polishing for tribological surfaces.
Aplikace: turbine seals, ventilová sedla, biomedical dental alloys (Co-cr), Noste komponenty.

9) Iron-based high-temperature alloys

What they are: heat-resisting irons (NAPŘ., Fe-Cr-Al, stainless steels formulated for elevated temperature).
Vlastnosti & výkon: cost-effective at moderate high temperatures, good oxidation resistance with suitable alloying.
Casting considerations & Aplikace: used where temperatures are high but extreme creep resistance of nickel alloys is not required (NAPŘ., díly pece, some industrial burners).

Special-purpose alloy castings

Precious-metal alloys (zlato, stříbro, platina)

What they are: Au, Ag and Pt alloys for jewelry, precision contacts and catalytic uses.
Vlastnosti & výkon: excellent corrosion resistance and aesthetic properties; variable mechanical strength depending on karat and alloying.
Casting considerations: nízké body tání (gold ~1,064 °C), Vynikající plynulost; vacuum or controlled atmosphere casting improves surface finish.
Investiční obsazení (Ztracený vosk) is the dominant manufacturing route for jewelry.
Aplikace: šperky, electronics contacts, decorative and specialty chemical uses.

Magnetic alloys (Al-Ni-Co, Nd-Fe-B variants)

What they are: permanent-magnet materials and soft magnetic alloys; poznámka: many high-energy magnets (Nd-Fe-B) are not commonly made by investment casting because powder and consolidation processes are typical. Al-Ni-Co can be cast.
Vlastnosti & výkon: magnetic coercivity, flux density and temperature stability determine suitability.
Casting considerations: magnetic alloys require controlled solidification to avoid unwanted phases; post-magnetization processing required.
Aplikace: senzory, motory, instrumentace.

Shape-memory alloys (Ni-Ti / Nitinol)

What they are: near-equiatomic nickel-titanium alloys with shape-memory and superelastic behavior.
Vlastnosti & výkon: reversible martensitic transformations produce large recoverable strains; used in actuators and medical devices.
Casting considerations: Ni-Ti is reactive and sensitive to composition; vacuum melting and precision control of Ni/Ti ratio are critical;
often produced via investment casting for complex geometries but powder-metallurgy and C-shape components are common. Post-cast heat treatment tailors transformation temperatures.
Aplikace: zdravotnické prostředky (stenty, staples), actuators and adaptive structures.

5. Závěry

Material choice is the single most influential decision in investment casting.

It governs not only the in-service performance of a part (pevnost, únava, koroze, teplotní schopnost, biokompatibilita, mše)

but also every practical aspect of manufacture: melting method, shell chemistry and firing, gating and feeding strategy, likely defect modes, required heat treatment and NDT, cost and lead time.

Klíč, actionable conclusions:

• Start with function, not habit. Define the dominating service drivers (teplota, koroze, nosit, únavový život, hmotnost, regulatory constraints)
  and let those map you to a material family (NAPŘ., nickel alloys for high-temperature creep, titanium for strength-to-weight and biocompatibility, duplex stainless for chloride service, bronzes for marine wear, precious metals for jewelry/electrical contacts).
• Match foundry capability to alloy demand. Many alloys (titan, Supermiony, Slitiny kobaltu) require vacuum or inert melting, HIP, and advanced NDT.
  Don’t specify an special alloy unless a qualified supplier can deliver and certify it.
• Design and process are co-dependent. Alloy attributes (rozsah tání, tekutost, srážení, reaktivita, segregation tendency, tepelná vodivost) must be used to set tooling compensation, gating/riser design, shell system and dewax/firing schedules.
  Early simulation and pilot castings materially reduce risk.
• Plan post-casting steps up front. Tepelné zpracování, HIP, surface finishing and machining affect dimension control and cost.
  Pro kritické komponenty, specify these steps in the RFQ (and include acceptance tests and traceability).
• Control quality by specification. Require MTRs, heat-treatment records, defined NDT regimes (radiography/CT for internal porosity, ultrasonic for thick ferrous sections, dye-penetrant for surfaces), and a clearly stated acceptance standard.
  Define limits for porosity, inclusions and mechanical properties.
• Balance cost, schedule and risk. Special alloys and stringent acceptance protocols increase lead time and cost.
  Use the simplest alloy that satisfies functional requirements and qualify alternatives where feasible.

Časté časté

Can any metal be investment cast?

Many metals and alloys are suitable (oceli, nerezové, superslitiny niklu a kobaltu, slitiny mědi, hliník, titan, drahých kovů).

Však, suitability depends on foundry capability: reactive metals (titan, hořčík) and high-melting superalloys require vacuum/inert melting and special shell systems.

Some magnet and powder-metallurgy alloys are not practical by conventional investment casting.

How do I choose between alloys when several meet performance needs?

Rank requirements (must-have vs desirable), then evaluate manufacturability (foundry capability, need for HIP or vacuum melt), náklady, lead time and inspection burden.

Pilot castings and life-cycle cost analysis help select the optimal trade-off.

Do all alloys need special shell materials or coatings?

Some do. Reactive or high-temperature melts (NAPŘ., titan, certain superalloys) may require inert face coats (zirkon, oxid hlinitý) and controlled firing to prevent metal-shell reactions.
Discuss shell formulation with your foundry during design.

How does alloy choice affect surface finish and machinability?

Metals like copper alloys and aluminium typically provide excellent surface finish and machinability; nickel and cobalt alloys are harder to machine and may require specialized tooling.

Stainless steels vary—duplex and PH grades machine differently than austenitics. Include machining allowance and tooling considerations in the design.

What about corrosion and environmental compatibility?

Corrosion performance is primarily a function of alloy chemistry and post-casting treatment (tepelná úprava, pasivace, povlak).

For aggressive media (chloridy, kyseliny), select corrosion-resistant alloys (duplexní nerez, slitiny niklu) and require relevant qualification tests (Pitting, SCC).
Environmental regulations (NAPŘ., RoHS, restricted elements) can also affect alloy choice.

How much more does a superalloy casting cost vs a steel casting?

Costs vary widely by alloy, complexity and post-processing.

Superalloys and reactive metals commonly cost several times more than common steels due to expensive feedstock, vacuum furnaces, HIP, and extended NDT.

Use total cost-of-ownership (materiál + zpracování + inspekce + výtěžek) rather than raw melt price alone.