Abstract: A fuel injector nozzle assembly comprises a nozzle defining a guide bore, a fuel pressurization chamber, a seat, and a nozzle orifice. A check valve member has an impact area and a guide portion. The guide portion slides within the guide bore to allow the check valve member to slide between an open position and a closed position. In the open position the fuel pressurization chamber is in fluid communication with the nozzle orifice. In the closed position the impact area of the check valve member is pressing against the seat of the nozzle, and the check valve member is blocking fluid communication between the fuel pressurization chamber and the nozzle orifice. The check valve member comprises a ceramic material having a coefficient of thermal expansion &agr;>8×10−6/° C. when averaged over a temperature range of 0° C. to 300° C.