IMemoryRelationshipClassFactory pMemRelFact = new MemoryRelationshipClassFactoryClass();
IRelationshipClass pRelClass = pMemRelFact.Open("TabletoLayer", (IObjectClass)pTTable, dbfJnField, (IObjectClass)pFeatLayer.FeatureClass, layerJnField, "forward", "backward", esriRelCardinality.esriRelCardinalityOneToMany);

IDisplayRelationshipClass pDispRC = (IDisplayRelationshipClass) pFeatLayer;
pDispRC.DisplayRelationshipClass(pRelClass, esriJoinType.esriLeftInnerJoin);

Type memRelClassFactoryType = Type.GetTypeFromProgID("esriGeodatabase.MemoryRelationshipClassFactory");
IMemoryRelationshipClassFactory memRelClassFactory = (IMemoryRelationshipClassFactory)Activator.CreateInstance(memRelClassFactoryType);
IGeoFeatureLayer gfLayer = pFeatLayer as IGeoFeatureLayer;
IRelationshipClass pRelClass = pMemRelFact.Open("TabletoLayer", (IObjectClass)pTTable, dbfJnField, (IObjectClass)gfLayer.DisplayFeatureClass, layerJnField, "forward", "backward", esriRelCardinality.esriRelCardinalityOneToMany);

IDisplayRelationshipClass pDispRC = (IDisplayRelationshipClass)gfLayer;
pDispRC.DisplayRelationshipClass(pRelClass, esriJoinType.esriLeftInnerJoin);

IMemoryRelationshipClassFactory pMemRelFact = new MemoryRelationshipClassFactoryClass();