How Are Titanium and Titanium Alloys Brazed?

Pure titanium is alpha titanium with a close-packed hexagonal lattice below 882.5°C and beta titanium with a body-centered cubic lattice from 882.5°C to 1,668°C. Brazing behavior depends on phase balance and heat treatment. Alpha alloys are stable, corrosion resistant, and readily brazed; alpha-beta alloys offer balanced properties; beta alloys are more prone to segregation and thermal instability.

Key Brazing Characteristics

1. A tough, stable oxide film must be removed and the cleaned surface protected until brazing is complete.
2. Heated titanium absorbs oxygen, hydrogen, and nitrogen, sharply reducing ductility and toughness; use vacuum or dry inert gas.
3. Heating near or above the alpha-to-beta transformation can cause beta grain growth and needle-like alpha-prime on rapid cooling.
4. Titanium reacts with many fillers. This improves wetting but can dissolve the base metal or create brittle intermetallic compounds.

Filler-Metal Families

Silver-, Palladium-, Aluminum-, and Titanium-Based Fillers

Silver fillers were the earliest widely used systems for titanium components below about 540°C. Copper additions reduce wetting as their level rises; 0.2–0.5% Li can improve it. Lithium also lowers melting temperature and helps remove oxide and nitride films. Ag-Cu alloys above about 15% Cu can form brittle intermetallics; Ni plus a small Li addition can improve joint strength and toughness.

Palladium improves wetting and high-temperature strength because it is mutually soluble with titanium and many common filler constituents. Aluminum-based fillers are useful where brazing must remain near an aging temperature. Titanium-based fillers use Ni, Cu, Zr, Be, or other beta stabilizers to lower melting temperature. They offer strong, corrosion-resistant joints but can aggressively dissolve thin base material or form brittle diffusion layers.

Amorphous Fillers and Process Control

Amorphous titanium fillers melt around 840–900°C, often at least 40°C below the beta-transus of common titanium alloys. Their uniform 30–50 μm foil form provides good wetting, flow, and joint consistency.

Degrease and remove oxide by blasting or appropriate acid cleaning. Braze in argon or vacuum using induction or furnace heating. Rapid heating and short holding times limit interfacial reaction layers; temperature and time must still allow the filler to fill the joint clearance completely.