Materials & Capabilities
Photochemical etching is not limited to soft or annealed metals. The process can successfully etch hardened alloys, heat-treated materials, and metals in their fully hardened condition using appropriate etchant chemistries and optimized process parameters. This capability represents one of the fundamental advantages of chemical etching over mechanical manufacturing processes, where material hardness directly affects tool wear, machining speeds, and manufacturing costs. Since photochemical etching removes material through chemical dissolution rather than mechanical force, the hardness of the material has minimal impact on the feasibility of the process.
Understanding this distinction is crucial for designers and engineers who might assume that hardened materials require annealing before fabrication and subsequent re-hardening after forming. With photochemical etching, components can be manufactured from pre-hardened material, eliminating heat treatment steps, preserving precise dimensions that might distort during heat treatment, and simplifying the manufacturing workflow. The ability to etch fully hardened materials expands design possibilities and enables applications where maintaining specific hardness and mechanical properties throughout fabrication is essential.
The fundamental principle underlying photochemical etching’s ability to process hardened materials lies in the mechanism of material removal. Chemical etchants dissolve metal at the atomic level through electrochemical reactions that break metallic bonds and convert solid metal into soluble ionic species. These chemical reactions occur based on the metal’s composition and the etchant’s chemistry, not on the material’s hardness, which is primarily a measure of resistance to plastic deformation and mechanical penetration.
When a punch attempts to shear through hardened steel, the tool experiences enormous forces and rapid wear because the hardened material resists mechanical deformation. The harder the material, the more force required and the faster tools wear out, making machining of hardened materials slow, expensive, and sometimes impractical. Grinding becomes necessary for many hardened parts, adding time and cost to manufacturing.
Chemical etchants, however, attack the exposed metal surface regardless of its hardness. A fully hardened spring steel, a precipitation-hardened stainless alloy, or a through-hardened tool steel all dissolve in appropriate etchants at rates determined by their chemical composition and microstructure rather than their hardness. While etch rates may vary slightly between annealed and hardened conditions of the same alloy due to microstructural differences, the variation is typically modest and easily accommodated through process timing adjustments.
One of the most common applications for etching hardened materials involves spring temper metals used for contact springs, flexures, clips, and other elastic components. These materials are supplied in their final hardened condition, with carefully controlled mechanical properties including yield strength, ultimate tensile strength, elastic modulus, and fatigue resistance. The spring temper provides the precise elastic characteristics required for the application.
Stainless steel spring tempers including 301, 302, and 17-7 PH are routinely photochemically etched in their fully hardened condition. These materials may have hardness values exceeding Rockwell C 40, making them extremely difficult to stamp or machine, yet they etch readily with ferric chloride. The finished etched springs retain their full spring properties without any degradation, ready for immediate use without further heat treatment.
Beryllium copper, phosphor bronze, and other copper alloy spring materials are similarly etched in spring temper condition. These materials are precipitation-hardened or cold-worked to achieve specific strength and conductivity combinations. Photochemical etching preserves these engineered properties while creating intricate spring geometries that would be prohibitively expensive or impossible to produce through stamping of such hard materials.
The ability to etch spring temper materials eliminates a significant manufacturing challenge. If springs had to be stamped or formed from annealed material and then hardened, the heat treatment process would cause dimensional changes, surface oxidation, and potential distortion that would require subsequent correction operations. By etching pre-hardened material, the finished springs emerge with precise dimensions and pristine surfaces, requiring no additional processing.
Precipitation-hardened stainless steels like 17-4 PH, 15-5 PH, and Custom 455 represent some of the hardest materials routinely photochemically etched. These alloys achieve their high strength through a heat treatment process that precipitates fine intermetallic compounds throughout the microstructure, dramatically increasing hardness and strength while maintaining good corrosion resistance.
In their fully aged condition, these alloys can reach hardness levels of Rockwell C 44 or higher, with tensile strengths exceeding 200,000 psi. Such hardness makes conventional stamping essentially impractical, as the forces required would destroy punches and dies rapidly. Machining is possible but slow and expensive, requiring carbide or ceramic tooling and generating significant tool wear.
Photochemical etching processes these hardened precipitation-hardened stainless steels efficiently using standard ferric chloride chemistry. Aerospace components, medical instruments, and high-performance springs manufactured from these premium alloys benefit from the ability to maintain certified material properties throughout fabrication. When material certifications document specific mechanical properties achieved through controlled heat treatment, photochemical etching ensures those properties remain unchanged in the finished component.
High-carbon tool steels and specialty steels in their hardened condition can be photochemically etched using appropriate etchant chemistries. While less common than stainless steel applications due to the materials’ tendency to rust and their typical applications in thicker sections, thin-gauge hardened steel components for specialized applications can be successfully etched. Etchants formulated for ferrous materials including ferric chloride or acid-based solutions dissolve hardened carbon steels reliably.
Applications might include precision shims or spacers where dimensional stability and hardness are both required, hardened filter screens that must resist wear while maintaining precise opening dimensions, or specialized components where the wear resistance of hardened steel justifies the material choice.
Titanium and its alloys, while not conventionally described as “hard” in the same sense as hardened steels, are notoriously difficult to machine due to their work-hardening characteristics, low thermal conductivity, and chemical reactivity with cutting tools. These properties that make titanium challenging to machine mechanically have no impact on chemical etching. Titanium alloys etch successfully using hydrofluoric acid-based chemistries regardless of their heat treatment condition or hardness level.
Aerospace-grade titanium alloys like Ti-6Al-4V in their solution-treated and aged condition, which provides optimized strength and toughness, etch as readily as annealed material. The ability to process titanium in its final heat-treated condition eliminates dimensional distortion concerns and preserves the carefully engineered microstructure and properties.
The capability to etch hardened materials provides several strategic advantages. Components can be designed using materials in their optimal condition without manufacturing compromises. There’s no need to specify softer materials that are easier to stamp but provide inadequate performance. Heat treatment distortion and the associated dimensional uncertainty are eliminated when parts can be etched from pre-hardened material. Manufacturing workflows are simplified by eliminating heat treatment steps between operations.
Quality control benefits from working with pre-hardened material, as material certifications and test reports apply directly to finished parts without questions about whether subsequent heat treatment was properly performed. This traceability is particularly valuable in aerospace, medical, and other regulated industries where material properties must be documented and maintained.
The ability to photochemically etch hardened metals, from spring tempers to precipitation-hardened aerospace alloys, demonstrates the process’s remarkable versatility and positions it as a uniquely capable manufacturing technology for high-performance applications where material properties cannot be compromised.
4020 Jeffrey Blvd. | BUFFALO, NY 14219
P: (716) 821-9393 / (800) 875-1093
Website by Luminus
