Investment Casting Materials — Choose the Right Alloy Early

1. خلاصه اجرایی

ریخته گری سرمایه گذاری (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 ریخته گری سرمایه گذاری. It determines not only the in-service performance of the finished part (قدرت, مقاومت در برابر خوردگی, پایداری در دمای بالا, زیست سازگاری, وزن),

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, روش های بازرسی, زمان چرخه, 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: خواص مکانیکی مورد نیاز (قدرت, سختی, خستگی), محیط عملیاتی (دما, رسانه خورنده),

هندسه (thin walls vs massive sections), تولید (سیالیت, freezing range, واکنش پذیری), post-cast processing (عملیات حرارتی, باسن), inspection needs and cost.

Ferrous alloy castings

1) Carbon-steel بازیگران

What they are: low-alloy steels where carbon is the primary strengthening element (به عنوان مثال, AISI 1020–1045, ASTM A216 WCB, معادل ها).
خواص & عملکرد: قدرت متوسط, 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.
پس پردازش: عادی سازی, خاموش کردن & خوی (بستگی به درجه دارد) to achieve desired hardness/strength.
برنامه های کاربردی: اجزای ساختاری, مسکن ها, general engineering castings where corrosion resistance is not critical.

2) Alloy-steel بازیگران

What they are: steels alloyed with Cr, مو, در, V, و غیره, برای بهبود قدرت, hardenability and elevated-temperature properties (به عنوان مثال, 4140, 4340 family analogs).
خواص & عملکرد: مقاومت کششی بالاتر, 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.
پس پردازش: critical quench/temper cycles, control of distortion during heat treatment. May require stress relief and tempering to balance properties.
برنامه های کاربردی: چرخ دنده ها, شفت ها, high-stressed structural parts, oil-field components.

3) فولاد ضد زنگ بازیگران

What they are: iron-based alloys with ≥10.5% Cr; families include austenitic (304/316/cf8/cf8m), مارتنزیتی (410/420), دوبلکس (2205) و رسوب سخت شدن (17-4 PH).

خواص & عملکرد: corrosion resistance ranges from general (austenitics) to high chloride resistance (دوبلکس/فوق العاده);
mechanical properties vary widely — duplex offers high strength + مقاومت در برابر خوردگی خوب; 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.
پس پردازش: آنیل راه حل, quench and aging (for PH grades); duplex may require careful heat treatment to keep phase balance. Passivation and pickling often follow machining.
برنامه های کاربردی: chemical plant components, دریچه ها, سخت افزار دریایی, sanitary parts, فرآوری مواد غذایی, دستگاه های پزشکی.

Non-ferrous alloy castings

4) Aluminum-alloy بازیگران

What they are: ال سی, Al-Cu and Al-Mg families (به عنوان مثال, A356, A357, ADC12, 6061-نوع) for cast components.
خواص & عملکرد: چگالی کم (~ 2.7 گرم در سانتی متر مربع), good specific strength (after heat treat for some alloys), excellent corrosion resistance when alloyed properly; هدایت حرارتی / الکتریکی عالی.
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.
پس پردازش: solution heat treatment and artificial aging (T6) برای قدرت; sometimes HIP for critical aerospace parts.
برنامه های کاربردی: محوطه هوافضا, automotive lightweight components, heat-dissipating parts.

5) مس-base alloys (برنز, برنجی, برنز آلومینیومی)

What they are: با اسن (برنز), مس-روی (برنجی), با (برنز آلومینیومی), با ما, و انواع.
خواص & عملکرد: مقاومت در برابر خوردگی عالی (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.
پس پردازش: annealing for ductility, machining is often difficult (سخت سازی کار); surface finishing and dezincification concerns for brasses exposed to certain environments.
برنامه های کاربردی: سخت افزار دریایی, اجزای پمپ, بلبرینگ ها, decorative and electrical parts.

6) تیتانیوم-alloy castings

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

Casting considerations: highly reactive melt (اکسیژن, 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.
پس پردازش: vacuum heat treatment, تسکین استرس, HIP common to close porosity for critical components. Surface finishing is important for fatigue-sensitive parts.
برنامه های کاربردی: aerospace structural components, ایمپلنت های پزشکی, high-performance sporting goods.

High-temperature alloy castings

7) Nickel-base superalloys

What they are: Ni-Cr-Co-Al-Ti based alloys (اینکونل, دوباره, Nimonic families) designed for strength and creep resistance at elevated temperatures (up to ~1,000 °C and beyond for some alloys).
خواص & عملکرد: 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; ذوب القایی خلاء, strict de-gassing and inclusion control are critical.
Directional solidification and single-crystal casting are specialized variants for turbine blades (different process chain).
پس پردازش: complex solution and aging heat treatments to develop γ′ precipitates; HIP and machining are common. Certification for aerospace sectors requires tight NDT.
برنامه های کاربردی: gas-turbine hot-section parts, هوافضا, تولید برق, 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 (به عنوان مثال, stellite family).
خواص & عملکرد: 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.
پس پردازش: solution/aging (where applicable), grinding and polishing for tribological surfaces.
برنامه های کاربردی: turbine seals, صندلی های سوپاپ, biomedical dental alloys (با هم همکاری), اجزای آن را بپوشید.

9) Iron-based high-temperature alloys

What they are: heat-resisting irons (به عنوان مثال, Fe-Cr-Al, stainless steels formulated for elevated temperature).
خواص & عملکرد: cost-effective at moderate high temperatures, good oxidation resistance with suitable alloying.
Casting considerations & برنامه های کاربردی: used where temperatures are high but extreme creep resistance of nickel alloys is not required (به عنوان مثال, قطعات کوره, some industrial burners).

Special-purpose alloy castings

Precious-metal alloys (طلا, نقره ای, پلاتین)

What they are: اوج, Ag and Pt alloys for jewelry, precision contacts and catalytic uses.
خواص & عملکرد: excellent corrosion resistance and aesthetic properties; variable mechanical strength depending on karat and alloying.
Casting considerations: نقاط ذوب کم (gold ~1,064 °C), سیالیت عالی; vacuum or controlled atmosphere casting improves surface finish.
ریخته گری سرمایه گذاری (موم گمشده) is the dominant manufacturing route for jewelry.
برنامه های کاربردی: جواهرات, 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; توجه داشته باشید: 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.
خواص & عملکرد: magnetic coercivity, flux density and temperature stability determine suitability.
Casting considerations: magnetic alloys require controlled solidification to avoid unwanted phases; post-magnetization processing required.
برنامه های کاربردی: حسگرها, موتورها, ابداع.

Shape-memory alloys (Ni-Ti / Nitinol)

What they are: near-equiatomic nickel-titanium alloys with shape-memory and superelastic behavior.
خواص & عملکرد: 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.
برنامه های کاربردی: دستگاه های پزشکی (استنت, staples), actuators and adaptive structures.

5. نتیجه گیری

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

It governs not only the in-service performance of a part (قدرت, خستگی, خوردگی, قابلیت دما, زیست سازگاری, جرم)

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.

کلید, actionable conclusions:

• Start with function, not habit. Define the dominating service drivers (دما, خوردگی, پوشیدن, زندگی خستگی, وزن, regulatory constraints)
  and let those map you to a material family (به عنوان مثال, 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 (تیتانیوم, سوپالیاژهای, آلیاژهای کبالت) require vacuum or inert melting, باسن, 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 (دامنه ذوب, سیالیت, انقباض, واکنش پذیری, segregation tendency, هدایت حرارتی) 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. عملیات حرارتی, باسن, surface finishing and machining affect dimension control and cost.
  برای اجزای حیاتی, 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.

سوالات متداول

Can any metal be investment cast?

Many metals and alloys are suitable (فولاد, ضد زنگ, سوپرآلیاژهای نیکل و کبالت, آلیاژهای مس, آلومینیوم, تیتانیوم, فلزات گرانبها).

با این حال, suitability depends on foundry capability: reactive metals (تیتانیوم, منیزیم) 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), هزینه, 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 (به عنوان مثال, تیتانیوم, certain superalloys) may require inert face coats (زیرکون, آلومینا) 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 (درمان حرارتی, منفعل شدن, پوشش).

For aggressive media (کلرید, اسیدها), select corrosion-resistant alloys (دوبلکس ضد زنگ, آلیاژهای نیکل) and require relevant qualification tests (سوراخ کردن, SCC).
Environmental regulations (به عنوان مثال, روه, 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, باسن, and extended NDT.

Use total cost-of-ownership (مواد + پردازش + بازرسی + بازده) rather than raw melt price alone.