By Mark Norfolk on Monday, November 15th, 2021
By Sarah Jordan
Cold spray additive manufacturing (CSAM) is a new process. It is based on traditional cold spray technology. The process works by accelerating powder particles to nearly the speed of sound. This gives the particles the needed energy to bond to a material.
CSAM has been adopted for use in repair. It is also used for component manufacturing. It is a solid-state process. This means that no melting occurs. Typically, the temperature is below 400℉. CSAM has been shown to work with most metals and alloys. It also can work with metallic glasses, metal matrix composites (MMCs), and even polymers. The process has several benefits including:
With such beneficial capabilities, CSAM is utilized in many industries. These include aerospace, defense, tooling applications, and more.
A problem with CSAM has been that the material can fall short of the expected properties. This is particularly true for harder metals which tend to have more porosity and less bonding. Attempts have been made to address this with post-processing. Current techniques, however, can cause cracks, distortion, and thermal-induced metallurgy problems. The application of heat is an issue for any CSAM that involves multiple metals. When heat is applied the two metals can diffuse into one another, creating undesirable brittle intermetallics.
Ultrasonic additive manufacturing (UAM) has recently been utilized as an alternative post-process technique. Normally UAM is used to consolidate metal foils into a solid piece of metal. The process uses high-powered ultrasonic vibrations (20,000 to 30,000 Hertz) in combination with downward pressure. This creates a friction bond that joins the foils together.
In the case of UAM as a post process, the metal foils were removed. The UAM head was used on the CSAM surface to further consolidate the cold spray material. The benefits of UAM as a post process are that it has similar characteristics to CSAM. UAM is also fast, has large build envelopes, does not require an inert gas or vacuum, has low energy use, and is a solid-state process.
In the study, cold spray was used to produce MMCs made of two blends of metal powders. The powders used were Cu-38Ni and CrC-30NiCr. Then UAM was performed on cold spray deposits to further consolidate the material. Testing included hardness, adhesive strength, tensile properties, porosity, and resulting microstructure.
The application of the UAM post-process showed great results:
This is an initial study to use UAM as a post process. The results appear very promising!