Forging titanium into intermediate shapes for forging stock can lead to poor surface quality or poor microstructure if not done properly.
Manufacturing titanium can lead to many problems, such as:
Twisting of small rectangles Edge cracking of rectangles
Surface cracking of beta alloy billets Strain induced porosity (SIP)
High sonic noise in forging stock Poor microstructure
Rolling Sheet & Plate
Wavy edges or center buckle on sheet Tearing and/or stretching of sheet
Anisotropic mechanical properties Crowning
Non-uniform gauge Poor recrystallization
Finishing Coil Products
Non-uniform pickling Oil contamination during pickling
Black spots Transverse lines across sheet
MATCO has the expertise to help with any problem you may encounter.
It is necessary to balance the proper amount of alpha/beta prestrain, beta recrystallization and final alpha/beta workout to obtain a desired final product. Proper die speed, drafts (reduction) and bite size is also important to drive work deep into the material and set up the microstructure for recrystallization and to eliminate die-lock or dead zones. Strict control over forging temperature is also critical because forging too far below transus will cause surface cracking and microstructural defects. Improper drafts and bites could lead to: 1) strain induced porosity (SIP) in the center of the billets, which could become failure initiation sites in final parts, 2) poor microstructure resulting in coarse and/or elongated primary alpha instead of fine equiaxed alpha, which will lower strength and ductility of the parts.
Rolling sheet and plate material with incorrect roll sizes, pressures or speeds can lead to sheets with defects such as wavy or torn edges, center buckling, or crossbow, to name a few. Rolls may need to be intentionally crowned in the positive or negative direction to eliminate some of these defects. Improper rolling temperatures and size reductions will affect recrystallization rates and microstructure, which in turn affect mechanical properties of the sheet or plate. Not enough work below the beta transus temperature will cause the mechanical properties will not be directional. If the rolling temperature is too low, the flow stress will not be high enough and the material may crack or split. However, if the rolling temperature is too high, frictional forces may be too low and roll slip may occur thus marring the material surface.
Thin gauge coil products are usually finished in an acid pickling bath to obtain the final desired gauge and produce a clean surface. Dark gray spots are indicative of non-uniform pickling and may be caused by oil contamination on the incoming coil. Non-uniform gauge across the sheet or through the length of the sheet may be due to poor balance of acids in the pickle bath or oxides on the surface resisting pickling in specific areas. The pickle bath must be continuously monitored and adjusted to maintain the proper concentration of hydrofluoric and nitric acids. The amount of free titanium must also be monitored as too much Ti+ will slow down the pickling process and prompt unnecessary acid additions. Dark black spots on the sheet surface are sometimes caused by the deterioration of the rubber rolls in the bath.
The Next Step...While MATCO has the expertise and the technology to unravel even the most difficult material failures, your input is vital for a complete analysis. By filling out the service request form and giving us a description of the problem, you can be sure that all aspects of your problem will be considered. We’ll send you a proposal for your work, including methods and costs. Solutions are just around the corner!