This work presents a study of the Spark Plasma Sintering of a boron and tungsten containing alloy (Ti49,92Al48W2B0,08, called IRIS) as a function of the sintering temperature. Microstructures of sintered alloys are analyzed by scanning and transmission electron microscopies. Investigations mainly focus on a fine near-lamellar microstructure. Attention is paid to both characteristic dimensions of this microstructure and orientation relationships between various phases. The fine near-lamellar microstructure is formed by lamellar grains surrounded by extended γ zones containing β0 precipitates. The size of lamellar grains ranges from 35 to 45 μm while the width of the borders remains between 5 and 10 μm. Effects of both boron addition and sintering temperature are studied. Orientation relationships between γ lamellae and γ grains in the borders, as well as between the γ matrix and the β0 precipitates are investigated. As a result of these investigations, a formation mechanism of this microstructure is proposed and discussed. The origin of the grain growth limitation during the SPS processing is particularly analyzed.