What is Grade 7 Titanium material

1. What is Grade 7 Titanium?

Grade 7 titanium, often called "titanium-palladium alloy," is a commercially pure titanium (CP Ti) variant modified with a small addition of palladium (Pd). It is standardized by organizations like ASTM International (e.g., ASTM B265 for sheet/plate, ASTM B348 for bars) and is primarily valued for its enhanced corrosion resistance-far superior to unalloyed CP titanium grades (e.g., Grade 2, Grade 4) and even many titanium alloys (e.g., Ti-6Al-4V) in aggressive chemical environments.

Unlike high-strength titanium alloys (e.g., Grade 5), Grade 7 retains the ductility, formability, and biocompatibility of pure titanium but addresses a key limitation of standard CP titanium: susceptibility to crevice corrosion and pitting corrosion in reducing acidic environments (e.g., hot hydrochloric acid, sulfuric acid). Its unique properties make it a staple in industries like chemical processing, pharmaceuticals, and desalination-where resistance to harsh chemicals is non-negotiable.

2. What is the chemical composition of grade 7?

Grade 7 titanium's composition is defined by strict ASTM standards, with palladium as the only intentional alloying element (added to boost corrosion resistance). Trace impurities are tightly controlled to avoid compromising performance. The typical composition (by weight) is as follows:

Element	Content Range	Role
Titanium (Ti)	Balance (~99.7%–99.8%)	Base metal, providing inherent ductility, formability, and baseline corrosion resistance.
Palladium (Pd)	0.12%–0.25%	Critical alloying element: Reduces titanium's electrochemical activity, preventing the breakdown of its oxide layer in reducing acids. It also enhances resistance to crevice corrosion in chloride-rich environments.
Iron (Fe)	Maximum 0.25%	Trace impurity; controlled to avoid weakening the alloy or reducing corrosion resistance.
Carbon (C)	Maximum 0.08%	Trace impurity; limited to prevent the formation of brittle titanium carbides, which reduce ductility.
Nitrogen (N)	Maximum 0.05%	Trace impurity; controlled to avoid forming brittle titanium nitrides, which degrade toughness.
Hydrogen (H)	Maximum 0.015%	Trace impurity; minimized to prevent hydrogen embrittlement (cracking under stress due to hydride formation).
Oxygen (O)	Maximum 0.20%	Trace impurity (also a mild strengthener); controlled to balance strength and ductility (higher oxygen increases strength but reduces formability).

This composition ensures Grade 7 maintains the workability of pure titanium while delivering the targeted corrosion resistance.

3. The Hardness of Grade 7 Titanium

Grade 7 titanium's hardness is comparable to that of other low-oxygen commercially pure titanium grades (e.g., Grade 2) due to its minimal alloying (only palladium, which has a negligible effect on hardness). Its hardness values vary slightly based on processing state (e.g., annealed, cold-worked)-the most common state for Grade 7 is fully annealed (to optimize ductility and corrosion resistance).

Key hardness metrics for annealed Grade 7 titanium (per ASTM standards and industry data) are:

Hardness Test	Typical Value	Range	Notes
Brinell Hardness (HB)	~110–130 HB	105–135 HB	Measured using a 3000 kg load and 10 mm diameter tungsten carbide ball (standard for titanium).
Rockwell Hardness (HRB)	~70–80 HRB	68–82 HRB	Uses the B-scale (100 kg load, 1/16" diameter steel ball), suitable for soft to medium-hard metals like CP titanium.
Vickers Hardness (HV)	~120–140 HV	115–145 HV	Measured with a diamond pyramid indenter; provides a more precise value for thin sections (e.g., Grade 7 sheet).

Notably, Grade 7 is not designed for high-hardness applications-its strength (typical tensile strength: 480–620 MPa) is slightly higher than Grade 2 (370–550 MPa) but far lower than high-strength alloys like Ti-6Al-4V (860–1100 MPa). Its value lies in corrosion resistance, not hardness or strength. Cold-working (e.g., rolling, drawing) can increase Grade 7's hardness (e.g., up to ~150 HB), but this is rarely done, as it reduces ductility and may compromise corrosion resistance in some environments.