From the NTSB Powerplants Group Chairman's Factual Report, UAL 1175,
https://data.ntsb.gov/Docket/?NTSBNumber=DCA18IA092
"The PW4000 112-inch fan blade has a hollow core airfoil. The blade is made from two titanium-alloy flat plates that have the airfoil’s external and internal features machined out. The airfoil halves then undergo dimensional and material inspections prior to being bonded together. The bonded halves undergo further machining and another material inspection prior to being formed into the fan blade’s final shape. After the blade is formed into the final shape, the blade’s root is machined as are the leading and trailing edges and the blade tip. The blade then undergoes a visual and another material inspection before undergoing several surface finish treatments. The blade then undergoes a dimensional inspection and a final inspection."
Not a very good or complete description
, but apparently diffusion bonded and superplastic formed.