How Is Titanium Brazed to Aluminum, Steel, Copper, or Ceramic?

Titanium to Aluminum

Aluminum-titanium structures combine low cost, high specific strength, and corrosion resistance, but their physical mismatch creates residual stress and brittle TiAl intermetallics. The filler must wet both sides, fill the clearance, and promote a multicomponent reaction that limits TiAl formation.

Al30Ag10Cu, Al10Cu8Sn, and Al10Si1Mg fillers have been used to vacuum-braze pure titanium to pure aluminum at 600–620°C. Their interfaces form TiAl3 with Ag2Al or CuAl2, or Ti7Al5Si12. The Al-Si-Mg filler produced the highest reported shear strength in this comparison, 70 MPa. Adding La and Pr to Al8.4Si20Cu10Ge enabled furnace vacuum brazing of Ti-6Al-4V to 6061 aluminum at 530°C and increased tensile strength to 51 MPa.

Titanium to Stainless Steel

Use vacuum or argon to prevent gas pickup and oxidation. Carbon, chromium, and nickel from stainless steel can react with titanium to form TiC, TiCr, and TiNi compounds. Select a filler below the titanium transformation temperature and avoid excessive brittle-phase-forming additions. For Ti-6Al-4V to 304 stainless steel, BNi7 showed the best wetting among 40Ti-20Zr-20Cu-20Ni, Ag-5Pd, BNi2, and BNi7; higher Ni content also restricted beta-phase growth. In air, silver filler with CuCl-AgCl flux plus a small LiF addition can improve wetting.

Titanium to Copper

Vacuum brazing Ti-6Al-4V to QCr0.8 chromium bronze with AgCu28 produces Ag and Cu solid solutions plus CuTi intermetallics. At 890°C for 10 minutes, the reported maximum shear strength was 449 MPa. Ti-Ni-Zr-Cu filler can join thin-wall Ti-6Al-4V to TU2 oxygen-free copper; a 10–20 μm nickel coating can restrict titanium dissolution. Braze welding directs heat toward the lower-melting copper side to limit titanium melting and TiCu formation.

Titanium to Ceramics

Ceramics resist heat, wear, and corrosion but are difficult to form and have low toughness. Brazing joins them to tough titanium structures, yet two problems must be solved: poor metallurgical wetting caused by ionic or covalent bonding, and residual stress caused by thermal-expansion mismatch. Premetallize the ceramic or add an active filler element, and reduce stress through a low-expansion reinforcement, an interlayer, or joint-geometry design.

Ag-Cu-Ti and Ag-Ti active fillers are common. Ag-Cu-Ti wets ceramics effectively around 850–1,000°C and can bond both substrates; above 1,000°C its ceramic wetting advantage declines markedly.