A process for investment casting a turbine wheel, comprising steps of: identifying a metal composition from which the turbine wheel is to be cast; providing a mold that defines a cavity into which the metal composition in molten form is to be poured for casting the turbine wheel, the cavity being configured for defining a hub portion of the turbine wheel and for defining blades extending from the hub portion; providing a seed member made of said metal composition, the seed member having an equiaxed grain structure; disposing at least a portion of the seed member within the cavity of the mold, the portion of the seed member within the cavity having a pin configuration and being disposed at a center of a region of the cavity that is configured for defining the hub portion of the turbine wheel; activating a heating device to pre-heat the mold and the seed member to a mold temperature within a range between a predefined minimum mold temperature and a predefined maximum mold temperature, followed by pouring the metal composition in molten form into the cavity such that the molten metal composition envelops the portion of the seed member within the cavity; and once the pouring is completed, discontinuing the heating by the heating device and allowing the metal composition to cool and solidify; wherein said portion of the seed member acts as a chill pin positioned at a center of the hub portion of the turbine wheel and able to absorb and dissipate heat via conduction along the length of said portion and as a source of small grain nucleation sites for the surrounding liquid metal during cooling, so that said portion of the seed member at least partially melts through contact with the molten metal composition and so that, upon cooling, the metal composition around the seed member solidifies with an equiaxed grain structure as precipitated by the equiaxed grain structure of the seed member. identifying a metal composition from which the turbine wheel is to be cast; providing a mold that defines a cavity into which the metal composition in molten form is to be poured for casting the turbine wheel, the cavity being configured for defining a hub portion of the turbine wheel and for defining blades extending from the hub portion; providing a seed member made of said metal composition, the seed member having an equiaxed grain structure; disposing at least a portion of the seed member within the cavity of the mold, the portion of the seed member within the cavity having a pin configuration and being disposed at a center of a region of the cavity that is configured for defining the hub portion of the turbine wheel; activating a heating device to pre-heat the mold and the seed member to a mold temperature within a range between a predefined minimum mold temperature and a predefined maximum mold temperature, followed by pouring the metal composition in molten form into the cavity such that the molten metal composition envelops the portion of the seed member within the cavity; and once the pouring is completed, discontinuing the heating by the heating device and allowing the metal composition to cool and solidify; wherein said portion of the seed member acts as a chill pin positioned at a center of the hub portion of the turbine wheel and able to absorb and dissipate heat via conduction along the length of said portion and as a source of small grain nucleation sites for the surrounding liquid metal during cooling, so that said portion of the seed member at least partially melts through contact with the molten metal composition and so that, upon cooling, the metal composition around the seed member solidifies with an equiaxed grain structure as precipitated by the equiaxed grain structure of the seed member.